There are tons of complaints in the forums that the Google PageRank went missing in action and is no longer working.
The issue is not with Toolbar PageRank, but rather how 3rd party tools lookup the PR values. Google did make a change, they changed the lookup URL for the PageRank value.
The issue, as explained well by David Naylor is that they changed the lookup URL.
So if you really want to check your toolbar PageRank, use Internet Explorer and it should work.
For the rest of us, back to work.