Had some trouble with appworld myself. Try to delete it from the handset, do a batt pull after that and go to BlackBerry - App World - Official Store for BlackBerry Apps
and install manually.
Accept the agreement and if it actually lets you navigate into MyWorld while there (even if nothing is showing) hold down ALT and press R S T (no need to be caps). This would reset your apps. My purchased apps were not showing before that and trying to buy again already purchased apps generated an error.