PolyCom VVX400 & EPM

I have EPM installed on a 2.10 Freepbx with VVX400 Polycom phones. We just installed the system last week. I programmed the phones using the EPM and they seemed to be working fine. Now the customer is complaining that the phones randomly freeze. Some calls that are transferred to a different phone will be lost. Any ideas as to what is going on? This is the first install we have with these phones.