[Exim] What type of resource is unavailable ?

Would somebody please confirm/reject my guess that the computer is out of
memory, based on this error message in exim_paniclog


2000-03-07 05:38:40 12SCeT-0008Ub-00 == xyz@??? T=smtp defer (-1):
fork failed for remote delivery to nier.org: Resource temporarily
unavailable
2000-03-07 05:38:40 12SCeT-0008Ub-00 == joe@??? T=smtp defer
(-1): fork failed for remote delivery to powernet.com.ar: Resource
temporarily unavailable



This is an Intel box with 256 Meg ram, 127 Meg Swap, Red Hat 6.1, Linux
2.2.14 and Exim 3.13

Thanks for any insights.

mark