I decided to downgrade from 2012 to 2011 version of NIS as I found the "new" Identity Safe is worth than the old version. It just won't work half as good as the old version, plus it became both annoying and - well - dumb. (the change in backup file format which made it unusable by other versions is one example).
Anyway, I was wondering if there is anyway to convert the new DAT file to NPM file, as my latest NPM backup file is 5 months old.
I take it you have already downgraded to 2011 then? Did you run live update repeatedly (rebooting as requested) after instaling 2011 until it reported no more updates? Also what version of Windows and SP do you have and is it 32 or 64 bit?
Yes, unfortunately the ID safe data format has changed between 2011 and 2012.
Please see the following post and see if this helps you.
The path to Norton Product Tamper Protection in the post I linked to was centric to 2012. For 2011 it is a bit different. Go to Settings > Misc. Settings > Product Security > Norton Product Tamper Protection and set to OFF as indicated in the reference post.