The above code error is what I get after upgrading to 1.5.0.1 - I have already tried re-installing the core files, tried dropping that table from the database, clearing cache and forcing a re-build of the table but still get the same error message. Both the frontend & admin areas are showing the error so there is no way into the backend at the moment.
I’ve got this same problem on my test server while trying to upgrade from 1.4.2.0 to 1.5.0.1 I’m sure there are many people with this problem. If I find any info I’ll post.
If you have already done an upgrade above 1.4.2 then run a restore of the DB and file system then you still may have tables that exist in the db that are not normally there in 1.4.2. Normally a DB restore is at the table level and not at the DB level - so you may have ended up with tables that where not deleted.
If you backed up your tables before upgrading to 1.5.0.1.or 1.5.1.0 use your 1.4.2.0 database. Otherwise if you had a failed install you no longer have a 1.4.2.0 database and reinstalling will get this error every time. If you did not back up the database you have no choice but to delete tables that were made during the failed 1.5 install. the problem is Magento did not write the MySQL updates to deal with the fact of existing tables (i.e. IF EXIST statement). if you have an old database you can compare them to figure out what to delete. See this thread http://www.magentocommerce.com/boards/viewthread/232650/ and you can have that for free