NewDocument returns null in SW2007 64 bit

I'm trying to prep a 64 bit version of our internal SW addin, but I'm running into a problem.  We use NewDocument with a number of company-standard parameters to create a drawing from a part.   This works just fine on a 32 bit machine, but in 64 bit the API call returns null.  Has anyone seen this?  Any idea why it might happen and/or how to fix it?SolidworksApi macros