Help:LinksysWRT300N vers. 2 firmware 2.00.20 loosing intenet after about 2 minutes

after upgrading from firmware 2.0017 to 2.0020 i have trouble with
the wireless connection to internet.
After i have been logged on in about 2 minutes i loose connection to
the internet.
there is still wireless connection to the router.
This has happended just after i upgraded, i had no problems before.
Can anyone help?

Regards