proftpd authgroupfile authentication acting odd

hi there,
im using the directives authuserfile and authusergroup but for some reason using the file for authusergroup causes proftpd problems
ive been struggling with this for quite some time now, any advice?

proftpd relevant config (proftpd.conf):
<IfModule mod_auth_pam.c>
AuthPAM on
AuthPAMAuthoritative off
</IfModule>
AuthOrder mod_auth_file.c
AuthGroupFile /etc/proftpd_group
AuthUserFile /etc/proftpd_passwd

the password and group file syntax i have checked and double checked,

after attempting to login i get:
421 Service not available, remote server has closed connection.
ftp: Login failed.

at this point /var/log/messages reads:

Nov 6 02:51:38 webserver /kernel: swap_pager: out of swap space
Nov 6 02:51:38 webserver /kernel: swap_pager_getswapspace: failed
Nov 6 02:51:38 webserver /kernel: pid 29197 (proftpd), uid 1002, was killed: out of swap space

this only happens when the contents of the specified authgroupfile is not empty.