anyone else tried the 5.3.5 fw on a 4x and using pots lines?

After we upgraded calls coming in on the pots line (line2, line is now not in use) phones would ring however when we picked up there was no audio and the caller would get a busy signal (I think this may have been the divert from the pots line being busy in the first place, to our sip line, however not sure). We also could make calls out (sip) however the called party got no audio we could here them.

Had to roll back to the old config fairly quickly and willl now have to plan a weekend upgrade a test unless anyone can shed some light?