Hi.
Check your inetd.conf file to ensure tftp isn't commented-out. If you have initiated the transfer via RCP, ensure that you've configured in accordance with the instructions shown here:
http://www.cisco.com/en/US/products/sw/cscowork/ps2073/products_installation_guide_chapter09186a00806a5dac.html#wp1026932
Something else that might be useful is to get a sniffer (or snoop) trace of the transaction to see what RME is using as logon credentials and how the 3750 is responding.
Any clues in:
/var/adm/CSCOpx/files/rme/jobs/swim/1569/sctb01aal1_telnet.log ?
Can you try the SWIM job without tacacs, and if so, is it successful? If you manually do the task (outside of RME), does that work?
as you can see (by the fact I'm kind of all over the place here), this error is somewhat generic in nature, so there are a lot of things to check.