Hi. My Site was PR 3 before this last update, but now i have PR 2. What are the main reasons for a lower PR ? Is it because of the CMS ? I was using mybb and now i changed to Wordpress...
No it would have nothing to do with changing your CMS. PR is all about your external backlinks. Over time it is natural to lose some backlinks. Also sometimes pages with your link gets archived and devalued. The sites linking to you could've also lost some of their own links, which makes their link to you count for a little less. To maintain and increase PR, you need to keep working at getting more backlinks.
That could explain it. Nobody likes to link to a site that doesn't resolve. Some of the links that pointed to your site might have been removed.
Keep checking the Google forum They normally show up once every 2-3 months. Do some decent link building and you'll be fine. PR is updated regularly, what you see in the toolbar is just an export.
Went from PR3 to PR1 on ozsource. The strange thing is whilst page rank dropped, traffic has tripled in the last 3 months since switching forum software to vbulletin.