ok cool, that might be the problem...
so here's what you'll do :
0 - go to a windows machine and make sure there is no internet explorer process opened (check the process manager)
1 - open WLM (offline)
2 - download and unzip ospy : http://projects.collabora.co.uk/~oleavr/oSpy/oSpy-1.9.6.zip
3 - open ospy
4 - go to menu capture->inject agent
5 - select msnmsgr.exe and click on 'Inject' (there are two 'inject' button, click on the one in the top, the 3rd button from the top, not the 6th one)
6 - a popup should appear, click ok, then click 'close' on the inject agent window
7 - go to menu capture->start
8 - connect in WLM
9 - once online, click on the inbox button
10 - go back to ospy, click stop
11 - go to menu capture->inject agent
12 - select iexplore.exe and click on 'Inject' (same button as in step 5)
13 - a popup should appear, click ok, then click 'close' on the inject agent window
14 - go to menu capture->start
15 - click *again* in WLM to go to your inbox, so you get a second internet explorer window opened.
16 - once you are redirected to the inbox, click 'stop' in ospy
17 - go to menu file->save
18 - save the ospy dump to a file, and send me that file to kakaroto AT users.sourceforge.net (precede subject with 'amsn')
19 - close internet explorer and WLM (completely, do an exit, or kill the process).
With that information, I'll be able to know exactly what's wrong with aMSN and the sha1auth.