Return of Reckoning

Data.myp:
System.Exception: You need to stop application currently using the following file: data.myp
at MYPHandler.MYPHandler.WriteFileToArchive(FileInArchive archFile, MemoryStream MS)
at MYPHandler.MYPHandler.ReplaceFile(FileInArchive archFile, FileStream newFile)
at RoRLauncher.Client ...