I experience no such problems. It is important, that on login you check the box below the credentials form.
Try the following: Login (with box checked), close the browser (remember to close all browser windows), start a new browser window and look for the phpbb2mysql_data cookie (for the tasvideos.org domain, ignore the phpbb2mysql_sid one). If it's still there you should be able to visit the forums page and be logged in automatically again.
If you paste the content of that cookie e.g. at
http://www.url-encode-decode.com/ and click decode, it should be of the following form:
a:2:{s:11:"autologinid";s:32:"32_characters_long_string";s:6:"userid";i:some_integer;}
and not
a:2:{s:11:"autologinid";s:0:"";s:6:"userid";i:-1;}
