Tools out there, including the Google toolbar, may use the same PageRank algorithm, but may fetch outdated results because they get the data from different Google data centers. This may explain the reason for different page ranks you may get from the same page.
Here’s more information from http://www.web-wise-wizard.com:
Google PageRank™ Complexities
Before we proceed it might be useful to say a few words about Google PageRank. A factor that is likely to confuse anyone who is new to Google PageRank is that there are effectively four different types of Google PageRank, Real PageRank, Toolbar PageRank, Toolbar Display and Directory PageRank. Adding to the confusion is the fact that Google has a large number of data centers scattered around the World that contain the PageRank databases and these databases are very rarely in sync with each other. This means that you will regularly get conflicting results returned by different data centers for the same PageRank query. Of the four different types of Google PageRank, Real PageRank is arguably the most important by far.
Retrieving the PageRank from Different Datacenters
One can check the status of a PageRank on various Google data centers by visiting: http://livepr.raketforskning.com
Google Page Rank Has Been Updated
There’s talk in the SEO blogworld that Google has changed their PageRanks and it may take a while to propagate on all datacenters around the world.
Google Page Rank Update Underway
Tim just alerted me to the fact that it seems Google are doing one of it’s periodic Page Rank Updates. These updates take a little while to show up on all data-centers around the world so it could take a day or two to shakedown – but you can read more about it in Digital Point’s PR Update has begun discussion and at WMW’s PR update Started.
Being a blog, this information is taken with a grain of salt, so it’s unclear how long (one day, one month, a few months) for the data to synchronize on all Google servers.
Here are more blog posts and pages about this PageRank Update. It also includes posts from what other people saying about it: