What message did you get?
Invalid certificate?
Certificate expire?
App incompatible to yourt version of Symbian OS?
If you have the first 2 problem, I suggest you to stop using self signed pirated app and buy the app. If you are buying the app and not pirating them, then contact the company/developer you bought your app from.
If you have the 3rd problem, find another version of the software and see if it support your version of Symbian OS.