This is just a short note about a gotcha I keep encountering with ADP taxware and then I neglect to document it, and it bites me in the a**. So here I am sharing my pain with the world (i should get a cookie).
ADP Taxware is a program that runs on a server. We have it running on our webserver with our website; currently our load allows this configuration. When the website calls the Taxware API, it needs access to the \program files\taxware directory. You MUST allow the internet anonymous account access to this directory or you will get an obscure error message, and stepping through the code will reveal it to be a permission denied error.
The only other quick advice I have to offer is make sure you copy your dlls to the system32 folder on your server; just residing in the taxware folder (where the install puts them) doesn't seem to be sufficient.
Finally, although Taxware's documentation is cumbersome, their tech support guy on this API is fantastic, his name is Jonathan Wang. Happy coding!