cdrecord can't get mmap on /dev/zero

[Graham Williams]

Using cdrecord 1.10a18-2 on an up to date Debian unstable installation
with kernel 2.2.18 (self compiled) trying to write to CD writer:

     cdrecord: Invalid argument. Cannot get mmap for 4198400 Bytes on
     /dev/zero

Any ideas what the problem is and a solution?

Many Thanks,
Graham