Members not able to play arcade

The Registered group has permissions to access and play, but a few members are still not able to play. The Registered group is their only usergroup.

do they see an error-message?

It says your usergroup does not have permission to play in the Arcade.

Still no luck in finding any issue why this is happening. :(

It was a browser issue it looks like and they only got access with the www part. Not sure if the others still have access.