Googlebot session ID crawling errors on forums

[Chetanmosaic]

The Scene is:-

I have phpbb forum integrated in my website. The issue is - In webmaster tool under crawl error section there were 250k+ erros mentioning url "not followed". These all url's have session id's. If i fetch them as google bot - the response code is 301.
If i am fetching the same url deleting the session id - the response code is 200.

Added: Googlebot can crawl without session id url's.

Please suggest as crawl error urls are increasing day by day.

The url's:-
with session id: example.com/forums/viewtopic.php?f=1&t=204800&sid=abde2ee4129b26a79bb847e7672d7784
without session id: example.com/forums/viewtopic.php?f=1

[lucy24]

Have you been to GWT and told it to ignore the sessionID parameter? This week it's under "Site Configuration" : "URL Parameters".

[g1smd]

When Googlebot visits your site, don't hand it a session ID. Likewise for other such bots.

This entails a modification to the PHP scripts running the site.