Do you have both analog ports registered? I have seen the error you are mentioning when the 1st analog port is registered but the 2nd analog port is not. The 2nd analog port is registered as a second device using a modified MAC address.
if the mac address for port 1 (the true mac) is:
001234567891
then the 2nd ports MAC address would be:
123456789101
basically remove the first two digits and add 01 at the end of the MAC
Once you have the 2nd port registered in Callmanager your event viewer messages should stop.
See the "Account information parameters" in the link below if you would rather disable the port on the ATA itself so it does not try to register with Callmanager:
http://www.cisco.com/en/US/partner/products/hw/gatecont/ps514/products_administration_guide_chapter09186a00800c4d1f.html#1007069
