If you are a Silverlight developer who likes to keep himself updated on the latest stuff around in technology then you might face this problem. Actually this happens when you upgrade your system to VS2010 , by update i don’t mean that you are changing the target framework to be used to .net framework 4.0 update here just means that your .csproj file now knows that it has to open itself with VS2010 but after sometime if you feel that VS2010 beta is unstable, which looked to me also then you want to revert back to old and tested VS2008 everything can be reverted back without problems but when you will build the project in VS2008 you will notice that it complains “Cannot get the list of output files from the project” this is because the ToolsVersion used is still 4.0 The simple solution is to just go to the .csproj file in any of the text editors and modify the ToolsVersion in every project in the solution which contains your silverlight project. Just replace the ToolsVersion = 4.0 with ToolsVersion= 3.5 and your solution will start working again. That’s it. Happy Programming!!!!!!!!!!!!!!!!!!!!!!!!!!!!