ERR: Failed to complete setup of assembly (hr = 0x8007000b). Probing terminated

My project is specificly 64bit.

I had to change a Reference to a dll, by adding the 64bit version. Creating a folder in my project called "x64" and adding the dll, with the property: Copy to Output Directory : Copy always

I found the solution in an Oracle readme:

Use the following steps for your application to use the 64-bit version of ....dll:

1. Right click on the Visual Studio project.
2. Select Add -> New Folder
3. Name the folder x64.
4. Right click on the newly created x64 folder
5. Select Add -> Existing Item
6. Browse to ...\bin\x64 under your project solution directory.
7. Choose ....64bit.dll
8. Click the 'Add' button
9. Left click the newly added ....dll in the x64 folder
10. In the properties window, set 'Copy To Output Directory' to 'Copy Always'.

For x86 targeted applications, name the folder x86 and add assemblies from the ...\bin\x86 folder.

My project/solution was the inverse of the fix here: I needed to un-check the "Use the 64 bit version of IIS Express for web sites and projects." I'm left assuming that the project is 32 bit, but the only release mode that broke for me was "debug". Viewing it in browser without debug never failed to compile.

I searched numerous questions for the solution, so I thought I would add my fix here. It does seem to work both ways (if it's checked, uncheck it!)

This is caused by trying to run a 64 bit process or dependency on IIS Express of 32 bit.

If you don't want to change for all your projects like suggested in @Shaun Roach's answer you can edit the specific startup project properties and change the Bitness in the Web tab to 64 bit, this will add <Use64BitIISExpress>false</Use64BitIISExpress> to your csproj (which by the way is not the same as the default <Use64BitIISExpress />).