Apple GS/OS Error Messages: Where to Find Explanations

I am trying to copy files from an Apple IIGS to an Apple HD40 SC. The Apple IIGS consistently returns the error message 8020. I cannot find this error message anywhere.

1) What is the error message?
2) Where can I find a definitive article on GS/OS error messages?
1) The error description is "invalid request." The programmer's constant is "DrvrBadReq". Since the error number is 8020 instead of 0020, the error is coming from the Finder, not directly from GS/OS. An error code directly from GS/OS would be in the format of "00xx". An error code passing through the Finder has the high bit set and produces a format of "80xx". Where "xx" is the actual error code.

2) Both Volume 1 and Volume 2 of the "GS/OS Reference" has an Appendix E containing the GS/OS error codes and the message related to that code. The individual system call description indicates which GS/OS errors that call may return. System Loader error messages are given within the System Loader call description section.
Published Date: Feb 18, 2012