Plugin manager not showing update notifications

I just upgraded from 2.3 to 2.5.1 and all went well. Going to the plugin manager, I was able to see quite a few plugin updates needed. I started updating then activating each plugin one by one. Now, for some reason, the update notices are no longer being displayed even though I know there are still some that aren’t up to date. I did try deactivating all the plugins to see if there was interference, but this did not help. I have logged into other blogs with the newest 2.5.1 version and they all seem to be displaying the notices with no problems. So, this is specific to this one installation. I have searched the forums for about an hour now and can’t find an answer. Any ideas?

Thanks in advance for your time!