...and which operating system are you using?...Vista or XP? It appears like you may be getting this error:

MSASCui.exe - Unable to locate component - reinstall MsMpRes.dll

When uninstalling Windows Defender from Windows XP, it's best to turn off and disable the Windows Defender "service" before using the "Add/Remove Programs" section.. It allows the uninstall to correctly take place.. In order to make sure Windows Defender is completely gone, have you tried the Windows Installer Cleanup Utility from the link below? If not, please do.

http://support.microsoft.com/KB/290301

In the meantime, if you haven't already, and because this might be the result of malware, please download, install, update, then run a full system scan using the free antispyware tool from the link below:

AVG Antispyware 7.5 Tool

Hope this helps and let us know more.

Grif