Mysterious "Unknown error [403]"

I'm having a problem with an Outlook add-in that creates an instance of PDFCreator 1.0.0 every hour.

Sometimes it issues the "An error has occured: Unknown error [403]" message box. When I click "OK" and the message box closes, the program continues and creates the PDF file like nothing bad had happened.

This error can happen too when opening the PDFCreator program interface. So, I thought the problem was the "check for updates" feature, and I disabled this.

But the problem arised again a few days after.

The system is WinXP pro, Outlook 2007 and the add-in is written in VB6.

Any idea.? Someone knows about this mysterious error?