I am not sure if Lynn and company have a way to downgrade or not, and I would wait until she confirms this or not.  If not, then the only way to get back to the previous version is to fully restore that backup.  The one problem would be that you would lose any activity since the backup.  
 
Now perhaps there is a way to restore just the executables and keep the database, but that is one you DEFINITELY need direction from Lynn.
 
Good Luck

Looking at your previous posts, it sounds like you had a problem with the update running properly, which unfortunately happens sometimes.  I would encourage you to try to call Lynn just to see if she is in this week, before you go thru the excruciating pain of redoing 3 days worth of transactions.  I know when I do updates, I encourage all users to try all transactions the morning of the update (if practical) to find any major blips (and only waste a few hours of transactions).
 
Good Luck

I just tried isapinv again. It does not run through the first DB. I don't know exactly how far it got the first time but I recollect at least several files being counted down.
 
Jon

We found and fixed a couple of problems.  Patch #2 is available at www.istechsupport.com/status.php and contains the files in Patch #1.  There were Binary Zero problems as well as Numeric to Text Conversion issues but it is fixed now.  If you have not yet downloaded the 12/21/08 update, the current file has been patched so you can download and install it without loading the patch files.
 
If you downloaded the update and ran the ISAPINV utility but it didn't finish (which is demonstrated by programs such as AP-B and AP-C telling you to run it when you aolready ran it),  restore the BKAPCHKH.B or BKAPCHKH.BXX where XX is the code for the company) file from before the update and re-run the utility after downloading the patch.