Hi,
I can't investigate for now, but you can try to delete the local folder (for windows: C:\Users\yourUserName\AppData\Local\Paint Of Persia\ ) and relaunch the program.
BUT save yours files before and C:\Users\yourUserName\AppData\Local\Paint Of Persia\User Data\Default\settings.json if you have palettes or anything you want to keep in program settings (replace the file after relaunch).