I've been having this problem in my Blackberry Curve 9300 since 2 weeks ago.
After I updated my Twitter app, I started having this problem: The applications (Twitter, Facebook, Viber and even the App World) won't run even if I'm connected to WiFi. Actually, it doesn't run with edge, 3G and GSM. My phone has to be on EDGE for them to run with WiFi, which I didn't need to have for them to run before.
I tried the hard reboot. It worked for 3 minutes max, with EDGE but once it returned to edge, it stopped working once again.
Again, I've never used a data plan before and it works, as long as there's WiFi coverage and I am happy with that until this problem happened. Hope somebody can help me solve this. Thanks in advance!