It has decreased because your backlink has been reduced and may be the pages where you had backlink have now been removed.. Work on to create more backlink for your pages.
PR depend on the number of quality backlink you have, you need to keep on building unique quality backlink for your site from time to time, in other to increase your backlink and get better PR in the next update.
Might be reason is backlink is reduced or outgoing links are more. for increasing page rank, do one thing give nofollow to all outgoing (External Links) and try to build quality links.
Just get more links and ignore pagerank. I have tried loads of different way of building links the best ones i have found is Article marketing through Submit Your Article and Forum posting through about 10 different forums with over 10,000 users and the newest i have found is submiting comments on blogs and articles through How to improve PageRank. Hope this Helps
Such problems can be more. Also when your website had penalty in SERP, it shows PR2. Actually this can be seen on the first PR update after that. Some days ago we had PR update, so maybe you lost backlinks, or the one you had now are with lower PR. PR is quite simple rating, but important only if you have revenue to the websites over the PR (I mean link sales). Otherwise traffic and profits are much more important.
intresting indeed I have seen sites with zero pagerank be higher in the serps than sites with pr 4 or 5...im not sure how important it really is...
Actually PR is showing the backlinks development of the whole website. This means - More Backlinks, higher PR. Of course not so simple, but this is the main picture. SERP or SEO Development of your website is related not only with number of backlinks (they are important), but also with inner pages development. So this means that if you did not built right SEO Strategy for certain keywords, even with high PR website you will not get good SERP. This is just basic knowledge
I think you must continue to build link everyday fluctuation of page rank sometimes happen so you must check your quality back links always.
Don't waste your time on pagerank, backlink building,... stuff like that.. As already said thousands of times here at DP.. Pagerank is useless. My PR6 gets daily about 1,500 uniques... and my PR 1 site gets around 20,000+ uniques daily.. so.. its all about the content, content... and the content!
The main factor that affects PR change is your site back links That could be the major reason for that change.
There are some reasons why pagerank of a site will decrease. Possible reasons are, your site decreases the number of backlinks or you have a paid links.
its just normal..continue to create quality and quantity links...because its one of the factors for having a good pr..