I wasn't able to find any claims that this software even tries to decrypt MsgPlus chat logs. In fact, it seems to have nothing to do with MsgPlus at all.
"View Yahoo and MSN chat logs without logging in to Yahoo or MSN."
http://www.fakewebcam.com/demoMYMA.asp
http://www.softpedia.com/get/Security/Decrypting-...coder-Viewer.shtml