MSN Messenger team member Leah has posted a new fix for Error 80048883 which prevents MSN Messenger 7.5 users from signing-in.

Here are the details of the work around for MSN 7.5:

1. Download the following file: http://clientconfig.passport.net/ppcrlconfig.bin - If you can't access the file, try downloading it from http://www.messengertools.net/Files/ppcrlconfig.dll
2. Change the file extension to .DLL (if not download from our site)
3. Now place the file into C:\Documents and Settings\[Windows Username]\Application Data\Microsoft\IdentityCRL\ and overwite the existing file.
4. Optionally reboot your computer.
5. Attempt to sign-in again using MSN Messenger.

Hopefully this will fix the problem, otherwise try visiting http://support.msn.com/eform.aspx?productKey=messenger&page=support_home_options_form_byemail&ct=eformts.