I have just had the same problems on our Solaris box, racking my brains trying to think if i had changed anything on the switches. Logged a call with our support co and they told me that RME tries a number of ways to back up the config, one way telnets onto the switch, and then tftp's the config to the NMS. Anyway, realised that when i was hardeneing the NMS box, i disabled tftp in the /etc/inetd.conf file. Re enabled this and now all works fine.
Patrick - BBC, UK