It looks like a temporary index file from an earlier Metamorph index update wasn't deleted (eg. the process died or was killed without a chance to remove it). A new update process happened to use the same temp file name, and expected the file not to exist. Remove any Tnnnnn.btr files, and re-issue the create/update index statement (you don't need to drop the index, but you need to delete these files).
On second thought, don't delete the Tnnnn.btr files; they could be live index files, because this is a Windows NT system (under Unix Tnnnn.btr files are always temporary, under NT they may be permanent). Just drop and re-build the index only.
