When removing Sopcast I got this error, and the uninstall would not complete, instead crashing out. I located uninst.exe and set the app compatibility mode to windows 98. To my surprise this worked, I expect it was built for a 32 bit version of windows.
The file name is part of the NSIS installer, and may also be reported as Bu_.exe or Cu_.exe etc, depending if there is duplicates in the temp folder.
Windows should remember the setting for the same program, but will not for other NSIS uninstallers, so keep this page in mind for next time.