[Solved] Can't get payment groups to work

I've read through several posts in the forums on payment group/subscription/donation problems and applied all of the fixes/advice, but I'm still having no luck setting up payment groups.
My Paypal configuration settings seem to be OK, because when a user clicks on the donate button they can actually donate to the site. It shows up fine in my Paypal account. When the user clicks on the "Return to Merchant" button, they are directed back to the lwdonateresult.php page.
The problem is that no record of the donation is credited to the user's account, nor does their donation show in the "donors" link or in the ACP - User Admin - Subscription page. Somehow the fact that they have donated never makes it back to the portal.
Secondly, I have set up usergroup as a payment group, and designated a minimum payment of $1.00. When a user clicks on Usergroups, they see the usergroup in the drop-down list, but when they click on the View Information button, they simply get a listing of the group members, with no button or method of joining that group.
Might anybody have come across these problems and perhaps be able to point me in the right direction?
My Paypal configuration settings seem to be OK, because when a user clicks on the donate button they can actually donate to the site. It shows up fine in my Paypal account. When the user clicks on the "Return to Merchant" button, they are directed back to the lwdonateresult.php page.
The problem is that no record of the donation is credited to the user's account, nor does their donation show in the "donors" link or in the ACP - User Admin - Subscription page. Somehow the fact that they have donated never makes it back to the portal.
Secondly, I have set up usergroup as a payment group, and designated a minimum payment of $1.00. When a user clicks on Usergroups, they see the usergroup in the drop-down list, but when they click on the View Information button, they simply get a listing of the group members, with no button or method of joining that group.
Might anybody have come across these problems and perhaps be able to point me in the right direction?