PROBLEM with incoming call on LT22i Xperia P

[fluke7]

I installed 3CX on LT22i Xperia phone. But when I try to accept on incoming calls, I can not answer the call. Answer key does not work. When i push on answer key the phone goes on silent mode and call from another phone comes in, but i can't answer. Outgoing calls, from LT22i Xperia, works good.

Please help me and thanks for help.
Regards Roi