|If you’re developing an assembly, placing it in the global assembly cache, and testing it from another application you probably want to keep making changes to the assembly, but don’t necessarily want to keep upping the version number (which means you will have to constantly change the reference in the testing application).
When dragging the assembly into c:\windows\assembly you may receive the error message
Even after deleting the existing file from the GAC you can still receive this error. What you need to do is go back to the good old command prompt. Click Start – Run and enter cmd.
Navigate to the directory where your assembly is stored
I found that when I deleted the assembly from windows, it removed the file but not the directory. Removing the directory from the command prompt resolved the problem and allowed me to drag my new assembly back in again.
In all honesty, you’re better off upping the version number for every change as this is more correct (and the way the GAC is intended to work), but if you do encounter the problem, then the above is the solution.