Dynamic update/nsupdate limitations

Hello,

We have been using dynamic update on small zones with great success
(1-10 records). However, recently I decided to try the technique on a
large(ish) zone of ~12,000 records. If I try to do an update of 13,500
lines I get the following error:

----- Output -----
dns_request_createvia3: ran out of space
------------------

Indeed I get the same error until I get to 2,500 lines, at which point
the update will work.

So, I thought, let's just try doing 6 updates of 2500 lines to update
the entire zone. The first four updates are progressed with success but
the fifth update fails with the same error:

----- Output -----
dns_request_createvia3: ran out of space
------------------

Anyone know why or how to configure bind or unix to increase this limit?

TIA,

Nick