When I update my blog I get a notice that an error occured and when I go to the activity log I get this:
Ping 'http://ping.blo.gs/' failed: Ping error: <string>Weblog hasn't changed.</string>

Anyone know why this might be happening?

same thing happend too me, I might search in the forums for an answer!

typically this happens if you update your weblog within a specific time interval for the ping service (I believe for blo.gs, it's 30 minutes).

if this happens to you all the time, I'd check your RSS and Atom templates index templates and make sure they're being rebuilt with the index files.

I usually pay very little attention to errors returned from the ping servers. They rank pretty low on the list of errors that need attention and correcting.