You are correct that V4 beta 9 included a fix intended to solve the same error (albeit seen with a different item). Clearly there is something unique and unanticipated about the KEY20.ITM file in your override folder. As a workaround, you can manually move that file out of your override folder while installing IR, then move it back into your override folder immediately afterwards. If you also attach the item file to your post here, someone may be able to determine the problem.