When i Log in Google Webmaster Tool and go to the "PageRank of your pages section", it says "Data is not available at this time.", its been like that for months and my site is a pr 5 and gets good traffic. Why do you think this is happening?
How often you get crawled? Does the webmaster section let you increase crawl-rate? R U indexed? Slow crawlrate (as in almost never) can do that. Make sure you're indexed first, and find better relevance links if you're not. That would be the first thing I'd check.
My site has PR ranking but in this site, it still say data not available. This has been going on since Day 1.