Bump Thread

[ZiNgA BuRgA]

^ I'm actually not sure how you managed to do that, since the plugin creates the field when activated, and drops it when deactivated.
The only possible causes I can think of:
1) somehow you messed up the plugins cache
2) you restored a DB backup before the plugin was activated, or, more likely, switched the threads table with an older one

I suggest just adding the "lastpostbump" field via phpMyAdmin (type etc doesn't matter; if you don't know how, ask your host), which will allow you to deactivate the plugin.  After that, reactivate the plugin.