Error accessing RF.jsp from the Forms in 11i: "Please use /OA_HTML/RF.jsp instead"

Recently came across this error after a clone, and found no info anywhere on it.  Whenever a jsp tried to launch from the Forms (View Approval Through Workflow, OAM, etc.), got a "Please use /OA_HTML/RF.jsp instead" message.

The issue was that there's a deprecated version of the RF.jsp in the $OA_HTML/jsp/fnd directory that was accidentally placed in the $OA_HTML directory.  Re-copying the $OA_HTML directory from Production solved the issue (I determined that the copy was done incorrectly; it may just be you need to copy a correct version of the RF.jsp from another $OA_HTML).