Permission problem after database migration from mysql 4.0 to 5.0

hi!

i want to upgrade wordpress from 2.8.6 to 3.0.3.

a prequesite to this upgrade is to advance the mysql version from 4.0.x to 5.0.x.

so i made a mysql dump from the mysql4 database. i created a new database on a mysql5 server and populated it with the data from the dump. after several tries i even figured out how to also import all special/foreigen characters correctly.
then i edit wp-config.php to point to the new database.

so far so good.

wp is able to connect to the new db.

but when i try to login i always and with all users and permissionlevels get a “You do not have sufficient permissions to access this page.”. in detail: i enter login and password, click “Log In” and on the next page (page profile.php) i get the above mentioned error message.

i have done a lot of search regarding this topic. please note, that the table prefixes did NOT change while migrating the database. they are “wp_” in the old and in the new database.
also the error occours right after login. not when trying to configure a plugin.

i lost a notable count of hair and a notebale count of hair turned grey while i tried to solve this migration problem. posting here and maybe in some newsgroup is my last resort.

any help AND an pointing into a direction or any guess is apprechiated.

thanks and regards,
art