I'm not clear on whether you're running the Macro from Excel or PPT.

Anyway, it's possible that the slide hasn't been opened and it's
bombing because of that.

You should check that the macro works in PPT - because it's possible
that M$ doesn't provide access to the PPT VBProject.

If it's a security thing, MS Office comes with a program for creating
digital certifcates called
Selfcert.exe. It allows you to create digital certificates.

For details see page 27 of "Microsoft Office 2007 Programming" for a
step through.

Or try Googling Selfcert.exe and see if you get lucky.