I'm using XOOPS 2.0.16.

When I enter with my username and password to my XOOPS site, and try to access a module as simple as "Contact" (directly through its URL) that I don't have permissions to, the system gets into an infinite loop with the message "You don't have permissions to .... If the page doesn't reload automatically, please click here..."

Of course I've previously entered to the admin page and modified the permissions of the registered users group unmarking the module "Contact" in the "module access privileges" section.

Can anyone try this and tell me if it is a system problem ?

You need to go into the admin group section and select "Anonymous" and then select each module you want to give access to.

Also, go back into the Registered group and give back the access to them, otherwise once a member is registered, they won't be able to use the contact form.