I have automotive kit users in our group on five continents. It is a rare issue that communication cannot be established through the parallel port. Most of those are caused by the PC hardware, or other resident software that uses the parallel port. Just having other resident drivers can cause issues. I suggest that the parallel port be dedicated to Pico only to avoid these issues. If it's a port hardware issue, like not having all the pins attached to the board, then the only solution is the USB adapter. This solves any parallel port connection issue.
None of this applies to the new four channel USB 2.0 automotive kit. They are pretty much plug and play. Had an issue yesterday with a new user establishing communication through a PCMCIA card USB adapter, on an older PC but got that one going without too much trouble. All the rest have been trouble free.
If you are in the US, feel free to call with any questions you might have. They don't call me the Picotologist for nothing
877-628-4899 toll free.