There is no difference, the Pagerank value you see in the toolbar and on Pagerank check websites and via scripts is called the "visable" Pagerank. This is updated every 3 to 4 months, however Pagerank is always changing real-time in the backend of things. The visable Pagerank does not actually represent the current value.
Basically there is no difference between these 2.. as Toolbar Page rank and Pagerank both are same... Google provides the toolbar with pagerank tool and the term pagerank is also been derived by Google only.
PageRank became widely known by the PageRank display of the Google Toolbar. The Google Toolbar is a browser plug-in for Microsoft Internet Explorer which can be downloaded from the Google web site.
im not an expert but as far as i know, pagerank is google's view of how important the site is, while toolbar pagerank is a toolbar that installed in our browser, but they're just the same.
PageRank - Is the measure of importance Google feels your page is worth. ToolBar PageRank - One of the greatest advertising gimics ever. The SEO community is based on it.