Vista - Please help - Live Messenger has become impossible to access

Hi all, I've registered here in a last ditch attempt for help on how to access my MSN Messnger. (I'm on Vista home premium 32 bit).

I've never had any problems at all untill I was forced to upgrade to the latest version. Now I can't even log in.

Here's the problem...

Every time I've signed in to messenger 8.5 for the last year or so, it's asked me if I want to upgrade. I've always said no, as the version I have has worked fine. But now a pop up box states that I have to upgrade or I wont be permitted to sign in.

So, ok I agree to upgrade. The download appears to complete, then rolls back and fails, every time.

The error code is Ox80070643 and the message is "Installer has insuficient privileges to modify this file... looks like another program is preventing the installer from working".

I've tried with my firewall turned off, cleared cache etc, but nothing works.

I've browsed the threads on this site and it seems to be a common problem. I've tried all the suggestions that I've read, including the very helpful suggestions and links from Jonathan Kay.

Is it a case of giving up with Windows Live? That seems crazy, as it was working fine before the forced upgrade!

Any help would be very much appreciated.

I'm having the exact same problem. I'm running Vista 64 Ultimate and I'm getting the same error number but a different message:

"Messenger couldn't be installed because we had trouble installing this requirement:

Microsoft Application Error Reporting. The Windows Installer Service could not be accessed. This can occur if the Windows installer is not correctly installed."'

I've tried everything but nothing is working. I've tried the steps posted here for this error message (Error 0x80070643 - Windows Live) but still no luck.

Hopefully someone can help!!