Failed to authenticate: Collection container is NULL

Hi,We recently upgraded our SMTP server (which is also an access point for remote users) to version R6.01 CF1, it worked fine for about two weeks and suddently we got a lot of the messages below:

06/17/2003 04:29:42 AM UserName/OU1/O from host [xx.xx.xx.xx:1668] failed to authenticate: Collection container is NULL

Rebooting the server solved the problem (temporarily) but if anyone has a more precise idea about what is going on, a solution or idea is more than welcome.

Thanks & Regards