When browsing around your folders you may discover files that start with the ~ character. These are security backup files written by the program. As you save a design file, Easy-PC will take a security 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 security copy, you should first rename the file to its proper name (using Windows Explorer) and then read that file instead.
For more details please see 'Configuring security copies'.