Below is an e-mail from MSN Messenger Support I found on Google. It worked for me straight away after lots of pointless reinstalling etc etc

I found that the thing that worked for me was the LAN settings – turning off Automatically Detect Settings allowed me to log immediately on!

It seems that messenger gets a lot of its config from IE which explains why the below fixed me.

Hacked? Trojan? No idea, I did find an address in the auto config script. http://autoconfig.interfusion.net.au:8082/servlet/net.interfusion.ai.pubproxy.ProxyConfig

No idea who they are or how they accessed my config settings.

Good Luck

__________________________________________________________

Thank you for writing to MSN Messenger Service.

You have been referred by Passport about your persisting
problem connecting to Messenger even after reinstalling
and creating a new passport account.

To resolve your issue, here are some things to try:

1. If you are running any third party software or have a
firewall such as Zone Alarm, you may want to disable those
applications and then try to log in to MSN Messenger –
sometimes third party applications will conflict with
other applications. If you are unsure how to do this,
refer to your third party application instructions or
help.
Note: Once you have successfully signed into MSN
Messenger you may re-enable your firewall.

2. You may need to update your Internet Explorer to the
latest version. To do so please go here:
http://microsoft.com/windows/ie/

3. Your IE security settings may need to be adjusted.
1. From the Internet Explorer menu, click “Tools” and
then click “Internet Options”.
2. In the “Internet Options” dialog box, open
the “Advanced” tab.
3. Scroll to the security setting section and ensure that
you have ‘check for server certificate revocation’
unchecked and that the ‘Use SSL 2.0’ and ‘Use SSL 3.0’ are
both checked, then click ok.

4. You may also need to adjust your proxy settings. To do
this:

First,

1. From the Internet Explorer menu, click “Tools” and
then click “Internet Options”.
2. In the “Internet Options” dialog box, open
the “Connections” tab.
3. Click “LAN Settings”.
4. Clear the “Automatically Detect Settings” checkbox.
5. Click “OK” to save the setting and then click “OK”
again.

Second,

1. On the “Tools” menu, click “Options”.
2. On the “Connection” tab, be sure the “I use a
proxy server” check box is clear. Because only certain
proxy servers require this, do not select this option
unless your network administrator tells you to do so.

To assist us in making MSN Messenger better for our next
release, please reply to this email and let us know which
(if any) of the above options resolved your sign in
issue.

For additional online help, please go to:
http://messenger.msn.com/Help/

Sincerely,

Ruby
MSN Messenger Support