Problems with Session tracking on Google

[Fortune]

The following was posted else where on the site, i never recieved a response so i thought i would post it here again. Appologies for the duplication
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I am having the problem with one of my clients sites.

The site itself is appoximatelly 6 years old, it has a Dmoz listing and for its Name i.e. search term it is ranked number on Google and all othe rmajor engines.

The site is built in ASP and makes use of session tracking.

The problem is this, only the home page is indexed and has a page rank. There are loads of other older pages example "page A" that simply is not indexed in google and does not have a page rank. However, "Page A" is indexed as a session (The site uses sessions to track sales from their affiliates and publishers).

Is the session tracking causing the problem? I.E has Google & Co indexed a session, then come across the actual flat page (no session) and say wait a minute, we have already indexed this page and thus not index the flat page.

If so, any thought on how this can be fixed? Im thinking of creating a Robot.txt file and exlcuding all sessions from being spidered by the Search engines.

Any thought's?

Thanks