It happens when Google update pagerank but I just downloaded Google toolbar this morning, I can see the pageranks of the sites.
Im seeing some wierd results as well... But it was working fine a few minutes ago... May just be a glitch
It may be a temporary problem as others stated, or as most of us would be hoping, it may be PR update!
Because I downloaded the google toolbar for the first time and wanted to see if it showed a difference between some other PR tools that are showing different results, and then noticed no sites were showing PR, not on the google toolbar, or with the LivePR, or SEO Quake plugin's for Firefox.
What's the URL(s) so we can check as well? By the way, don't get caught up in the PR frenzy...PR means nothing...SERPs mean everything. The "little green bar" doesn't show Google's ACTUAL PR.
I know it doesn't mean too much. I have a PR1 ranked #1 in Google with over 30,000 searches a month. haha, site below me is a PR5. But it is always something to keep in mind. The PR stuff seems to be fine now... no more problems here.
Sometimes, page rank toolbar and tools experienced these kind of scenarios. But after few hours or days, it returns on its right numbers.