I also ahd this problem but don't run S2U2. What caused it for me was Diamond Tweak or Advanced Config tool - changed a registry setting and it wouldn't answer calls. fixed the reg entry and all is good. Now trying to remember the reg entry.....
"There are numerous thread about this issue...it has to deal with the HKLM/Comm/ConnMgr/Planner/Settings "SuspendResume" value which changes upon the install of AC/DT.
Default setting is #777"
From thread:
http://forum.ppcgeeks.com/showthread...t=answer+calls