There was a mistake in the Visual Basic (VB) function declarations for the specific WDU_TransferXXX() functions in WinDriver\vb\include\wd_utils.cls, which explains the problem that you encountered. In addition, this file contained two redundant function declarations (WDU_GetDescriptor — which does not exist, and WDU_GetDeviceData — which is a lower level function that is not implemented for VB, and is not generally required).
To resolve these problems, either upgrade to version 6.0.1 (or newer) of WinDriver or download the following modified file from v6.0.1 of WinDriver: wd_utils.cls and copy it to the WinDriver\vb\include directory in place of the file from the original v6.0.0 distribution.