Do you have tcl/tk installed?
From the amsn FAQ
Q: What do I need to run amsn?
A: Amsn is written in tcl/tk, so you just need a working tcl/tk interpreter
(version 8.3 or later). You can get it at http://tcl.sourceforge.net.
interpreter is available for linux, windows and macintosh.Some additional
features might require extra programs or libraries, like the docking icon,
the Display Pictures or the SSL connection for MSN Protocol 9.