refused query on non-query socket from

We are an ISP and using Bind 8.2.2-P5 on Solaris 8. Since long time we
are getting following error messages.

named[346]: [ID 295310 daemon.notice] refused query on non-query
socket from [212.x.x.x].53

We don't have any problem in DNS operations but few of our clients
with MS Exchange servers some times complaints that they have
intermittent DNS resolution problem which causes delays in their
outgoing emails. usually they got timeout errors. I am afraid that is
there any link in between this timeout complaints and the refused
query error mention above.

I have read many replies on this issue but still need more information
that does it effect the DNS performance and how I can get rid of this
error.

I hope I will get a positive response.