Attaching to running powerpoint instance

Hi,
Is there a way for me to attach my c# application to a previously
running powerpoint instance? My code of:
PowerPoint.ApplicationClass ap = new PowerPoint.ApplicationClass()
works fine if there isn't an open instance of powerpoint (or if that
instance has been previously created from the above line) but fails
with the error below if powerpoint is previously open.

"Retrieving the COM class factory for component with CLSID
{91493441-5A91-11CF-8700-00AA0060263B} failed due to the following
error: 80080005."
Source="**"
ErrorCode=-2146959355

Thanks,
Bob