Ever get that error that says the compile can't be completed due to some other process holding on to a .dll - but not know what process is holding on to it?  Go to http://www.sysinternals.com/ and download the Process Explorer and find out what process is using it.  You can do a search for the dll name to speed things up.

BTW: sysinternals has an RSS feed now at http://www.sysinternals.com/sysinternals.xml