Unable to load Add-In Avast! 4 and was disabled by Outlook

Hi guys,
The problem is with my Microsoft Office Outlook. It stopped working throwing the error message as under whenever I wanted to open it. I have no idea of the error message. If you have any idea for the issue, please help.
Thanks in advance.

Microsoft Office Outlook
The Add-in “avast! 4”(C:Program FilesAlwil
SoftwareAvast4ashOutxt.dll)cannot be loaded and has been disabled
by Outlook. Please contact the Add-in manufacturer for an update. If no
update is available, please uninstall the Add-in.
