This error often rears its ugly head when compiling an ASP.NET 2.0 Web Deployment Project. At first glance, it is extremely difficult to troubleshoot because there is not much information along with the error. In order to troubleshoot this, you need to use a higher level of verbosity. If you're using MSBuild from the command line you can use the /verbosity switch like this (and then look at Output window for build): C:\projects>msbuild YourSolutionFile.sln /t:Rebuild /p:Configuration=Release /verbosity:detailed ......