Like Nick, I've found that deleting *.ncb files seems to cure almost every problem I have with the IDE. I don't use any VCS system yet but I make zip backups of my source directories at least once a day. I've got the batch file that does the zipping setup to delete any .ncb files, among others, before it makes the archive. Be aware that the *.ncb file is locked while the project is loaded in the IDE. I seem to recall that the IDE occasionally fails to release the file lock when you close a project from the File menu. I now just exit the IDE to make sure that everything is closed properly.