I too am having these problems that started when I installed Plus - I have just installed 3.52 and still get problems.
I have Zone Alarm, although I do not think this is the issue.
I have worked out that when it looks like it is signing in for ages, if i select an option on the "Always sign in as: " drop down list, MSN appears ot sign in - although no contacts are shown. Although I cannot see my contacts - they can still send me messages and I can reply. From here I cannot sign in or out - I must exit the program.
When I sign in using Windows Messenger I have no problems.
Also, I have noticed that if I sign in to Windows Messenger, and then sign in to MSN 7.. at precisely the point when Windows Messenger tells me I'm signed in somewhere else, if i change the "Always sign in: " status to Online, then MSN 7 signs in successfully - showing me the contact list.
For thos wishing to try this method - it takes few attempts to get it right
Hope this helps Patchou,
Good luck
Andy