C# .NET Missing Method Exception when opening ZipArchive created with System.IO.Compression

I have a C# WinForms .NET app in which I'm trying to write to a zip archive and read from it using System.IO.Compression.

Here's now I create the ziparchive:

    public void SaveStdV20ZipProject(string strfilepath, clsProjectInfo GameInfo)
    {
        using (var ms = new MemoryStream())
        {
            using (var archive = new ZipArchive(ms, ZipArchiveMode.Create, true))
            {
                string strProjectData = String.Empty;
                StringBuilder sb = new StringBuilder();

                // First, we add the Game Info data...
                sb.AppendLine(GameInfo.strGameVersion);
                sb.AppendLine(GameInfo.strProjectType);
                sb.AppendLine(GameInfo.strGameTitle);
                sb.AppendLine(GameInfo.strAuthor);
                sb.AppendLine(GameInfo.strCreationDate);
                sb.AppendLine(GameInfo.blTSImagePresent.ToString());
                sb.AppendLine(GameInfo.blTSAudioPresent.ToString());
                sb.AppendLine(GameInfo.blTSVideoPresent.ToString());
                sb.AppendLine(GameInfo.blFSSImagePresent.ToString());
                sb.AppendLine(GameInfo.blFSSAudioPresent.ToString());
                sb.AppendLine(GameInfo.blFSSVideoPresent.ToString());
                sb.AppendLine(GameInfo.intTotalQuestions.ToString());
                sb.AppendLine(GameInfo.intTotalMediaItems.ToString());
                sb.AppendLine(GameInfo.intTotalCategories.ToString());
                sb.AppendLine(GameInfo.blTiebreakerPresent.ToString());

                // Next, create an archive entry for the Game Data string...
                strProjectData = sb.ToString();

                var ProjectData = archive.CreateEntry("ProjectData.txt");

                using (var entryStream = ProjectData.Open())
                using (var streamWriter = new StreamWriter(entryStream))
                {
                    streamWriter.Write(strProjectData);
                }

                // We're done writing all the data for this project. Now let's write it to the file...
                using (var fileStream = new FileStream(@strfilepath, FileMode.Create))
                {
                    ms.Seek(0, SeekOrigin.Begin);
                    ms.CopyTo(fileStream);
                }
            }
        }
    }

And here's how I open it:

    public void OpenStdV20ZipProject(string strfilepath)
    {
        string zipPath = strfilepath;
        string extractPath = Path.GetTempFileName();

        using (ZipArchive archive = ZipFile.OpenRead(zipPath))
        {
            foreach (ZipArchiveEntry entry in archive.Entries)
            {
                if (entry.FullName.EndsWith(".txt", StringComparison.OrdinalIgnoreCase))
                {
                    using (StreamReader sr = new StreamReader(extractPath))
                    {
                        clsProjInfo.strGameVersion = (string)sr.ReadLine();
                        clsProjInfo.strProjectType = (string)sr.ReadLine();
                        clsProjInfo.strGameTitle = (string)sr.ReadLine();
                        clsProjInfo.strAuthor = (string)sr.ReadLine();
                        clsProjInfo.strCreationDate = (string)sr.ReadLine();
                        clsProjInfo.blTSImagePresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.blTSAudioPresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.blTSVideoPresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.blFSSImagePresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.blFSSAudioPresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.blFSSVideoPresent = Convert.ToBoolean(sr.ReadLine());
                        clsProjInfo.intTotalQuestions = Convert.ToInt32(sr.ReadLine());
                        clsProjInfo.intTotalMediaItems = Convert.ToInt32(sr.ReadLine());
                        clsProjInfo.intTotalCategories = Convert.ToInt32(sr.ReadLine());
                        clsProjInfo.blTiebreakerPresent = Convert.ToBoolean(sr.ReadLine());
                    }
                }
            }
        }
    }         // <-THIS IS LINE 1320

It throws a Missing Method Exception and I've looked high and low in the Internet for a fix. Here's the stack trace:

System.MissingMethodException occurred
  HResult=0x80131513
  Message=Method not found: 'System.IO.Compression.ZipArchive       System.IO.Compression.ZipFile.OpenRead(System.String)'.
  Source=TASv20ClsLib
  StackTrace:
   at TASv20ClsLib.clsOpenStandardProject.OpenStdV20ZipProject(String strfilepath) in C:\Users\Reuben\Documents\Visual Studio 2017\Projects\C# Projects\TRIVIA AUTHOR SUITE V20 PROJECTS 2\TAS v20 Zip Test Jun14 2\TASv20ClsLib\Class1.cs:line 1320
   at Trivia_Author_v20.frmMain.openV20ProjectToolStripMenuItem_Click(Object sender, EventArgs e) in C:\Users\Reuben\Documents\Visual Studio 2017\Projects\C# Projects\TRIVIA AUTHOR SUITE V20 PROJECTS 2\TAS v20 Zip Test Jun14 2\Trivia Author v10 New Approach\frmMain.cs:line 1627
   at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)
   at System.Windows.Forms.ToolStripMenuItem.OnClick(EventArgs e)
   at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
   at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
   at System.Windows.Forms.ToolStripItem.FireEventInteractive(EventArgs e,     ToolStripItemEventType met)
   at System.Windows.Forms.ToolStripItem.FireEvent(EventArgs e, ToolStripItemEventType met)
   at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
   at System.Windows.Forms.ToolStripDropDown.OnMouseUp(MouseEventArgs mea)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.ToolStrip.WndProc(Message& m)
   at System.Windows.Forms.ToolStripDropDown.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at Trivia_Author_v20.Program.Main(String[] args) in C:\Users\Reuben\Documents\Visual Studio 2017\Projects\C# Projects\TRIVIA AUTHOR SUITE V20 PROJECTS 2\TAS v20 Zip Test Jun14 2\Trivia Author v10 New Approach\Program.cs:line 126

The ZipFile.OpenRead(string) method was added only in .NET 4.5. It does not exist in previous versions.

Your question is not clear about which version of .NET your project targets, nor which version of .NET is installed where you are trying to run it, but undoubtedly, you have targeted .NET 4.5 or higher, but are trying to run the code on which only an older version of .NET is installed.

To fix this, either make sure .NET 4.5 is installed on the machine where you want to run the code, or use the older API. For example, you can write your own OpenRead(string) method without much difficulty:

ZipArchive OpenRead(string filename)
{
    return new ZipArchive(File.OpenRead(filename), ZipArchiveMode.Read);
}
}