Found the problem. There's an error in the usb_tc08.vh file, which incorrectly removes the tc08 part of the name from the header, which is stopping the call from completing successfully. TO fix, open up the usb_tc08.vh file and change this line:
short __stdcall usb_get_formatted_info (short handle,
short __stdcall usb_tc08_get_formatted_info (short handle,
Save the file, and now call the correctly named function. Pico engineers, you might want to update the SDK with this fix, and any others that may have been found by others in the past.