Seems goofy, but add the bold text shown below.
Also, I would recommend changing the current working directory to your outdir, passing only the
file name as the FileName parameter of Export, and then returning the user to the previous working directory when you're done. The reason for this is the FileName parameter for Export only accepts 40 characters. You could run into an issue if you have a many characters in your working folder path.
Dim dwginstructions As IpfcDWGSetupExportInstructions
Dim exportInstructions As IpfcExportInstructions
Dim outdir As String
dwginstructions = (New CCpfcDWGSetupExportInstructions).Create()
exportInstructions = CType(dwginstructions, IpfcExportInstructions)
outdir = asyncConnection.Session.GetCurrentDirectory() + model.InstanceName.ToLower + ".dwg"