Recently I updated the Internet Explorer on one of my SharePoint Development Servers to IE 10. Since then I wasn’t able to script debug directly in Visual Studio 2010. The problem was whenever I tried to attach to the Internet Explorer process I got the error message that a debugger is already attached to this process.
The reason for this problem can be found in the wrong registered “msdbg2.dll” of IE 10. What needs to be done is to re-register the dll in 32-bit mode.
First start the cmd.exe in 32-bit mode. For this you need to run “C:\Windows\SysWOW64\cmd.exe”
In the command line execute the following command to re-register the dll.
regsvr32 “%ProgramFiles%\Internet Explorer\msdbg2.dll”
Once this is done restart your Visual Studio 2010 and now the debugger should be able to connect again to the Internet Explorer process.
The solution for this I found with some luck at Microsoft Connect and worked well for me.