Outlook 2007 Issue

[tfrank]

Windows XP Pro SP3, Microsoft Office Professional 2007.

Sometimes when replying to different emails in Outlook 2007, after I click
the SEND button, the following error message appears:

"An error occurred in the underlying security system. The supplied handle
was invalid."

This does not happen all the time, just once in a while and with different
people. Can someone point to a cause for this and how I might be able to fix
this issue?

Thanks