This error often caused by add-ins installed by Norton security products, but if you have an Acer computer, the eDataSecurity add-in for Outlook may be the cause. Note that these two applications are the most well-known cause but other applications may cause it as well.
Unloading the offending add-in will usually fix it, if not you'll need to uninstall the application.
In Outlook 2003, go to Tools, Options, Other tab, Add-ins, location the offending add-in and disable it. In Outlook 2007, you'll go to Tools, Trust Center, Add-ins. If its not listed, you'll need to edit the registry.
- Open the registry editor (Start menu, Run, type regedit)
- Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins
- Locate the suspected add-in in the list
- Set the LoadBehavior to 0
In most cases, disabling the application's integration won't affect your usage of Outlook and often makes it run smoother, but if you need Outlook integration, check the vendor for updated versions. Note that you do not need Antivirus scanning of your email – Outlook's security blocks active content and all attachments are written to the hard drive prior to opening so they can be scanned by the autoprotect feature of antivirus software.