FAILURE - out of memory in start

[bashr]

Messages like the following are regularly logged on this server for each 
of the four installed hd's:
+ad4: FAILURE - out of memory in start
They did not occur before implementation of a gmirror of gstripes. 
Occurrances of failures do not correspond with times of heavy load. 
Such failures were mentioned on freebsd-geom in Aug 2005, but without a 
resolution that I could find. Setting vm.kmem_size_scale=2, as suggested 
elsewhere does not solve the problem.

Any advice or suggestions will be much appreciated.  Here is some more info:

 >gmirror status
         Name    Status  Components
mirror/gm0s1  COMPLETE  ad2s1
                         ad4s1
                         ad6s1
                         ad8s1
mirror/gm0s2  COMPLETE  stripe/st1s1
                         stripe/st0s1

 > gstripe status
         Name  Status  Components
stripe/st1s1      UP  ad2s3
                       ad4s3
stripe/st0s1      UP  ad6s3
                       ad8s3

 > mount
/dev/mirror/gm0s1a on / (ufs, local, soft-updates)
devfs on /dev (devfs, local)
/dev/mirror/gm0s2a on /var (ufs, local, nosuid, soft-updates)
/dev/mirror/gm0s2d on /tmp (ufs, local, nosuid, soft-updates)
/dev/mirror/gm0s2e on /usr (ufs, local, soft-updates)
/dev/mirror/gm0s2f on /usr/home (ufs, local, nosuid, soft-updates)
linprocfs on /usr/compat/linux/proc (linprocfs, local)

 > uname -a
FreeBSD ***.***.*** 6.2-PRERELEASE FreeBSD 6.2-PRERELEASE #0: Tue Dec 12 
13:30:20 EST 2006     ***@***.***.***:/usr/obj/usr/src/sys/GENERIC  i386