1.2 is very old, not supported here and has many security problems. If you want to be hacked at least twice a day due to these bugs, suit yourself.
If you don't like 1.6, what's wrong with using the latest version in the 1.4 series???
There are no problems with 1.6.
Well, seeing as we don't support 1.2 here, and haven't done for well over a year and a half, we can't support you with this. And even if we did help you downgrade, we wouldn't be able to support you in future, as we don't support 1.2 here, so you'd be on your own either way. Sorry. You should have taken a file and database backup for an upgrade as big as this, you'll need to revert to those backups, and if you didn't take backups, then there's nothing we can do, you should have taken full backups for an upgrade as big as this. 1.6 offers nothing but improvements over 1.2, but if you want to stay with 1.2 forever, you'll be on your own with it.