(Resolved in 2.2.0)

A program is trying to access e-mail addresses you have
stored in Outlook. Do you want to allow this?
If this is unexpected, it may be a virus and you should
choose 'No'.

This was a known issue in the addin's signature insertion engine that was fixed in the 2.2.0 release. The only known workarounds were either to disable signature insertion or to update to a different version of Microsoft Outlook (both 2000 and 2003 and later did work).