How to fix a probable bad upgrade / How to start from "scratch"?

Friends,

I've been having some issues with what seems to be a bad upgrade (as I posted here: http://punbb.org/forums/viewtopic.php?id=8049&p=3 ).

Here's what I said, "I just tried to upgrade to 1.2.6 and even though everything seemed to go smoothly (uploaded all the files, ran the upgrade script and got the message that the DB was upgraded correctly) but my forum still says version 1.2.5 ???

I tried to run the upgrade script again and it said not a supported version (which means that it must think I'm at version 1.2.6)?  Any ideas what is going on?"

It isn't a local cache issue.   I was going to just leave it alone until I started to notice some other issues recently. 

For example, when I try to put the site in "Maintenance mode" I get "Error: Unable to write configuration cache file to cache directory. Please make sure PHP has write access to the directory 'cache'. "

Also, when I try to add a new forum I get "Error: Unable to write quickjump cache file to cache directory. Please make sure PHP has write access to the directory 'cache'. "   Even though I got this error the forum is created???

When I try to delete that new forum I get: "Error: Unable to write quickjump cache file to cache directory. Please make sure PHP has write access to the directory 'cache'. "

I've TRIPLE checked all the permissions for the directory and the files, but no dice.

?s:
1) How can I fix these problems and get from 1.2.5 to 1.2.6?   
2) Are these two issues (the cache issue and version # issue) related?
3) If I can't fix these problems, is there a way to take all the data in my DB and apply it to a fresh clean install?

Thanks in advance for your help!!!
Here is the forum:
http://www.nifty-stuff.com/forum/index.php