Trying to access excel COM object as admin user

The objective is to access the running Excel workbook in the machine. Intention is to close the respective workbook though this application which was opened by the user.

Achieved: I used the following code snippet to access the Excel COM object

        Excel.Application instance = null;            
        try
        {
            instance = (Excel.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");
        }
        catch (Exception ex)//Excel not open
        {
            wasFoundRunning = false;
        }

        if (wasFoundRunning)
        {
            foreach (Excel.Workbook ss in instance.Workbooks)
            {
                string s = ss.Name;                    
            }
        }

Issue: Above code works only if the excel sheet and the application opened by the same user in the machine. I have to run the application as administrator and it fails. Exception as follows and it means that it cannot find any excel sheet running.

Exception:  Operation unavailable (Exception from HRESULT: 0x800401E3 (MK_E_UNAVAILABLE))

It fails if I run my application elevated and user opens the sheet.

Any ideas to fix this?