can't lock /etc/mail/aliases

[aphro@portal.aphroland.org]

im getting this on a buncha systems when i run 'newaliases'

mail:/etc/mail# newaliases 
warning: cannot lock /etc/mail/aliases: Error 0
/etc/mail/aliases: 332 aliases, longest 63 bytes, 12743 bytes total

but according to lsof nothing is using it:

mail:/etc/mail# lsof | grep /etc/mail/aliases
mail:/etc/mail# 

even when i shut the mail server down(sendmail) i still
get the can't lock aliases file.

most of the systems are running sendmail 8.9.3 but this
particular one uses 8.11.3 (all of them experience that
warning)

doesn't seem to be harmful but wanted to know if there is
a way to track down what could be locking it.

thanks

nate