There are many reports of people not being able to get PageRank values across different DC's. This doesn't look like a bug to me, I think that Google may have pulled the plug on us using these tools.
It has been that way for while now (few weeks) so I was thinking the same. Its very hard to find working pagerank checkers that check different datacenters these days..
Digpagerank was working for me yesterday, and now doesn't seem to be doing anything. Also, my serprank site which does checks on Google ( and other search engines ) for SERP results is constantly coming back as blank for Google, whilst continuing to work for the other search engines. It does look like something is up with allowing us to interact with Google at the moment - hopefully it's just a temporary glitch though.