Hi Asif!
Firstly - I'd suggest that as soon as possible you address the core problem - the use of session ids in the URL. There are not many upsides to the approach and there are many downsides.That it doesn't show up with the site: command doesn't mean it isn't having a negative impact.
In the meantime, you should add a rel=canonical tag to all the offending pages pointing to the URL without the session id. Secondly, you could use robots.txt to block the SEOmoz bot from crawling pages with session ids, but it may affect the bots ability to crawl the site if all the links it is presented with are with session ids - which takes us back around to fixing the core problem.
Hope this helps a little! 