There is a binary object in the application library named appname.pra that contains the icon filename and the default fonts & colors.
If the pra is corrupted, you need to start by creating a new target with a new library with an appname that is the same as the appname in the corrupt target. Then exit PB and do some library file renaming so that the new app/library becomes the app/library for the main target. Then copy all objects from the old library. A new pra will be created the first time you do a save in the application painter.