redispatching of failed stateful request

When I use the Web Dispather, When we open some page in my portal, it will get some 500 error.There are some error log in my Trace file.

[Thr 2315] Tue Dec 18 00:46:56 2007

[Thr 2315] *** WARNING => redispatching of failed stateful request [http_route_m 3021]

[Thr 773] *** WARNING => redispatching of failed stateful request [http_route_m 3021]

Then I check the parameter of the webdispather. I see

wdisp/redispatch_foreign_sessions = TRUE

Can anybody help me to solve this urgent problme? Thank you very much!!!