Did you upgrade the vcware when you went from 12.0 to 12.1? If you did, that would probably explain the problem. 12.1 ios is supposedly backwards compatible with previous versions of vcware. 12.0 ios is not compatible for instance with vcware version 6.08. So if you upgraded your ios to 12.1.2T and upgraded your voice feature card vcware to 6.08, then reinstalled 12.0 it shouldn't work well at all.
What version of 12.1 are you using? Some serious changes came about in 12.1.5 regarding how calls setup when talking to a switch which means you need to add some new commands to make it compatible with the way earlier versions handle call setup. We have currently at least 5 different version of ios running...for various reasons. We put 12.1.5T on 3 5300s in order to resolve serious bugs with cas signalling. We have had some 12.0.7T and 12.1.2T versions on the network at the same time. All 12.1.7T have been upgraded to 12.1.2T or a 12.1.3T version. Make sure you have the proper vcware for your version of ios....
show vfc 1 version vcware and show vfc 2 version vcware. With 12.1.2T, you should have 6.08. Cisco claims that any given version should be compatible with a previous version of vcware.....but that is not necessarily the case. It will work but may not work the best. If you do upgrade your vcware and or ios and vcware...all of the commands on Cisco's site are wrong. It is copy tftp vfc: Trust me, you will save hours of troubleshooting or one or two tac cases if you listen to me regarding the copy command when upgrading vfcware. Also, make sure you know what dsps you are using. I believe 549 will enable you to run 96 high complexity codecs on a 5300. If possible use the vcware software with the hc in it...standing for high complexity as opposed to the mc medium complexity codecs. Tac has told me that 12.1.5T is by far the most stable version of ios for the 5300 and our experience indicates that to be true. Problem is they recommend 128 megs of ram. If you don't do more than 48 voice ports....64 megs will probably be okay, but you are potentially asking for trouble if you don't upgrade to more ram. Are you using cas lines as opposed to pris? An ios bug will show all lines busy and new calls can't be made....even when people who were using the line successfully hang the phone up if you have cas signalling. Check the Cisco site for caveats for 12.1.5t. That document will show resolved bugs for 12.1.2T, 12.1.3T, and 12.1.5T and will show unresolved bugs for 12.1.5t. I believe all of this stuff is potentially related. Hope I have helped in some small way.
Cheers,
Jim Cornelson
