Question about error message "multiple RRs of singleton type"

I am receiving the following error on my secondary nameserver when it
tries to transfer a specific domain:

Jul 30 10:29:33.219 transfer of 'ZZZZZZ.com/IN' from 111.11.111.1#53: failed 
while receiving responses: multiple RRs of singleton type
Jul 30 10:29:33.220 transfer of 'ZZZZZZ.com/IN' from 111.11.111.1#53: end of 
transfer

Without knowing for certain, I am guessing this is caused by multiple
CNAME RRs for the same hostname (there are two sets of them).

If there is something else to look for, please let me know.
Thanks,
Chris