I’ve recently been suffering with a problem using the latest version of Windows Live Messenger (WLM/MSN) which was when I was signing in I was prompted with an error code of 8100030D, I tried the usual stuff like reinstalling WLM and reverting back to an older version of WLM with no luck. I was confident I could fix it today and managed to do it. I will try my best to explain what I did and hopefully help others. If you try these please bear in mind that I am using Vista 64bit with Service Pack 1.
Here’s what I tried and what eventually worked:
What worked for me:
- Deleting the contents of C:\Users\AppData\Local\Microsoft\Windows Live Contacts
What I tried and could possibly work for others:
- Checking the time and date of my PC to make sure it was correct.
- Disabling any Firewall
-
- Running these commands in “Run”
- regsvr32 softpub.dll
- regsvr32 wintrust.dll
- regsvr32 initpki.dll
- regsvr32 MSXML3.dll
- Telling WLM to forget your current user’s saved password
Hopefully can assist at least one person 
If it’s where Messenger just throws an error with no helpful message I disable Vista’s TCP Auto Tuning feature.. works great then and lets me sign in.
I had this same problem myself. It lasted about 8 months for me.
I the problem ever persisted after formatting, and installing a different OS. In the end, I gave up and started using Pidgen for windows.
About 4 months ago, I finally found some help online, and deleted the contents of the folder you deleted, as well as a couple others, and have never had a problem since!
Basically, when it started was after updating to a bete build of the software, while MsgPlus plugin was already installed. Dunno if that has anything to do with other peoples troubles?
Thanks for the reply EvilWalks, it is possible that I upgraded to a beta version which could have caused it. Great to know the root source of the issue!