Google has made an update in its PageRank that is making troubles to some webmasters. We are not referring to the June 24th update but to a newer one.
You can find discussions on this topic in WebmasterWorld's thread also in Google Webmaster Help threads, but there are many others out there.
In the Google Webmaster Help, user TeaMan asked:
"we take care of a website www.goodtea.eu which had the Google page rank value of 2 about a year ago. Since a certain moment in time it has been assigned a value of 0. There were no major changes to the web site. Is there a way to find out why the web site has been assigned a page rank of zero?".
Googler JohnMu, replied to one webmaster saying that he/she should not worry about the last PageRank change because it was likely a "technical quirk":
"You have a nice-looking site :). As far as I can tell, it looks like the change in Toolbar PageRank for your site is only due to some technical quirk and not something that you need to worry about".
JohnMu has then been asked if the PageRank's "Technical Quirk" is somewhat widespread... but up to date he has not answered...
There are some rumors that Google has adjusted their link algorithm to look more at how "relevant" the link is to the page it is linking to.