This is kind of answered here http://www.nch.com.au/ivm/modems.html
Voice Modems End-of-Call Detection problems
Some voice modems incorrectly detect the end-of-call tone. On the IVM, use the "End-Of-Call Tone Detection Settings" (on the Settings - Devices tab) to correct defects. (a) If the modem does not detect end-of-call when it should, tick the Enable Software Based Detection box. ( If the modem detects end-of-call when it should not (and therefore hangs up), untick the enable detection during playback option
Your problem is when you updated IVM it reset the parameters on the modem driver. You will have to go into telephoney devices, go to properties of your telephoney device, and try different settings there. The first 2 settings are the key ones to fix this, try different combinations of these until you hit the right one.