Was the application and MTDLL installed under elevated Administrator privledge?

>I have an app that sends emails using a MTDLL that I created which uses an ActiveX mail control. It does this using the VfpMtApp (multithreading DLL) so that I can send mail and continue normal program processing. It's been tried and true under Windows XP, but under Vista it fails - well, sort of. The mail gets sent fine, but the thread never completes. I've tracked it down to the RETURN statement within my MTDLL code. If I run the MTDLL directly (outside of the multi-threading) I see the error, which is OLE IDispatch Code 5.
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>Does anyone have any idea why this would fail running under Vista but not XP?
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>Thanks,
>-m@