When browsing around your folders you may discover files that start with the ~ character. These are backup files written by the program. As you save a design file, Easy-PC will take a backup copy of the existing file under a name starting with ~.
In general, you should not read back in and work on designs starting with ~. If you need to restore this backup copy, you should first rename the file to its proper name (using Windows Explorer) and then read that file instead.