Screen sharing and login

I've got a mini running Leopard and a MBP running Snow Leopard. I'm trying to use screen sharing in finder to connect to the mini from the MBP. There seems to be something preventing screen sharing whenever a user is logged in to the mini, even if the login occurs in screen sharing.

Here are some examples of the behavior:

If I'm logged in as "macuser1" on the mini, I can connect to the mini as "macuser1" or "macuser2" and see folders, etc in Finder, but, when I click the share screen button, I get a connection failed message.

If I go to the mini and logout, then go to the MBP and connect to the mini as "macuser1" I can see folders just fine. When I click share screen it connects just fine and I see the login screen on the mini. If I enter a username and password it logs in just fine (I can see it logged in on the mini), but screen sharing from the MBP says "reconnecting" and can't connect anymore.

Something about being logged in on the mini prevents me from sharing its screen.

I tried creating a new user account without success. I could log into the new account, but as I was logging it, I got the "reconnecting" screen on the MBP (but could see that the login worked on the mini).

I've got all the right users in the screen sharing part of sharing settings.

Any ideas?