A few days ago, the attach button in "Attach to process" dialogue became disabled in VS 2010 and VS 2008 likewise. At first I thought that it is just an extension I've installed in VS 2010 but then I noticed it is the same in VS 2008. The both VS's a re running in administrative mode and on Windows 7. I looked around but I can't seem to find a solution to this. If anybody has encountered an similar problem, a little help would do great. Thanks upfront.
EDIT: Attached a picture of the dialogue!
Where it says
you should press 'Select' and ensure at least managed is ticked. (or choose automatic)
otherwise, the 'Attach' button will be disabled.
I have come across a weird situation under which Attach button was disabled. This was because of DebugDiag. Please refer the following thread for info.
It could also be because there is already another debugger attached to the process - probably the currently running instance of Visual Studio but it may be another instance of Visual Studio, or another debugger entirely (such as WinDbg or a remote debugging session).
Check the "Processes" window (usually found under Debug -> Windows -> Processes) to see what processes Visual Studio is debugging.
Try stopping Visual Studio but don't close the process.
I was trying to debug a windows service as described here and had the same issue. The solution was to run Visual Studio as Administrator and select to see processes from all users.
来源：https://stackoverflow.com/questions/5529476/vs-attaching-to-process-disabled