You receive error code 80048051 when you try to sign in to Messenger?  Try these steps:

Disable compatibility mode for Visual themes

  1. Click Start, (My) Computer.
  2. Browse to the folder C:\Program Files\Windows Live\Messenger.
  3. Right-click the file msnmsgr.exe, and choose Properties.
  4. Switch to the Compatibility tab.
  5. Uncheck the checkbox at “Disable visual themes”.
  6. Click OK.
  7. Retry to sign in to Messenger.

Disable Internet Explorer Offline mode

  1. Open Internet Explorer (even if Firefox or a different browser is your default browser).
  2. Click File, and uncheck the option “Offline mode”.
  3. Close Internet Explorer.
  4. Retry to sign in to Messenger.

(i) These tips did not resolve your issue?  Consider contacting the Windows Live Support.

Source: http://messengermaximal.spaces.live.com/blog/cns!40F43EC9BA81D814!7381.entry

Related posts:

  1. Messenger problems: Affected by Offline mode
  2. Messenger problems: Solving Messenger error code 81000306 at sign-in
  3. Messenger problems: Cannot sign in, no error code