Cyril wroteLet me explain the situation again,
When I used What'sApp for the first time through wifi it worked fine.
After I left the wifi zone, & came back again, I tried using What'sApp and it did not work.
I had to remove my battery so the phone would do a hard reset so it would work again.
It's a really annoying thing.
I tried this solution before posting here on the forum and it didn't work.
Thanks anyway Babum for your reply.
had the same problem , i just upgraded my firmware (bb 9780)