I've been experiencing this for about 2~3 weeks now.  When I'm talking with my friends, sometimes I don't receive their messages.  It doesn't show any error for either me or them.  It's as if they never typed to me at all.  I noticed this usually occurs I idle from WLM for a period of time, doing my own thing in the background(around 5mins+ or more).  Then later, they would wondered if I got their messages.  It never happens when I'm constantly talking with them.

I have the latest version of WLM aside from the beta.  I've done re-installs multiple times and I've tested it with AIM and other IM applications.  It only seems to be affecting WLM.

This problem is quite frustrating.  WLM is my favorite IM and I'd hate it if this problem drove me away from it.  Any help would be gladly appreciated.

What security software are you running? Firewall, anti-virus, internet security, etc.

Security applications are known to block access to WLM - try removing them and seeing if the problem continues.

I'm using Avira AntiVir Personal and Windows Firewall.

I'll try removing/turning these off, thanks.

Have a read of I cannot send Instant Messages to my Windows Live Messenger contacts from the Windows Live Solution Center. Following the instructions and removing any Messenger add-ons should solve your problem.

If no luck, try a clean install. Instructions from CookieRevised here or Windows Live Solution Center here

No go so far.  I turned off my Firewall first.  Then I uninstalled Avira, still no progress.

I've attempted to do a full clean uninstall and reinstall last week, but that didn't work either.  Uninstalled all tool bars and such as well.

If you try WLM from another computer, do you still lose mssages?

Unfortunately I don't have another computer to test WML.  I doubt it's WML itself.  I'm pretty sure it has something to do with my computer or routers' settings.

Just to put it out there, I'm using Vista and my router is Linksys WRTU54G-TM.

If you take out the router and just use a direct connection to the internet with an ethernet cable, do you still have problems?

Here's instructions how to open ports in your WRTU54G-TM router settings, however make sure you use this list of updated ports for WLM 2009.

I use the ethernet cable 80% of the time. 

I restarted my router, as in wiped settings back to default.  The frequency of those "lost messages" seem to be happening less now.

I can't seem to get port forwarding working correctly.  The PortforwardPortchecker program tells me it's not open.  I'll keep trying and update you on it.

Maybe it's a problem with the quality of your line?

Packet loss: 0%

Ping: 92

Jitter: 6

Grade B connection.