Recently few of our developers and me got this error while building my Silverlight application. I got this error while checking in the code and merge my code changes.
Error Details.
Error 38 The "CleanRiaClientFilesTask" task failed unexpectedly.
System.ArgumentException: Illegal characters in path.
To resolve this we need to do two simple steps.
Step 1: Go to this location in your system or your Framework install directory, for me its C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files. Clean all the temporary files under this location and leave the root folder empty.
Step 2: Go to your project location and Delete all the files in \obj folder. Basically all the files are stored in the \obj folder created by ria services.
Now clean the project and try building again. It worked for me. Hope this will help you. Good luck
