I had a similar problem on previous versions of CMSMS (see my old and sadly neglected post:
http://forum.cmsmadesimple.org/index.php/topic,16334.0.html) and have the same issue on sites upgraded to 1.2.3
No real solution so far, a clean install of 12 live client sites is just not an option as a solution I'm affraid.
I have 2 early sites that haven't yet been upgraded running 1.0.6 that don't have this problem and 1 later running 1.2 that is also mysteriosly fine. Another 3 sites running 1.2 have the problem and all recent upgrades to 1.2.3 have the problem also.
I can't see what is different or what the common denominator is between the sites that do and those that don't.
Here is an attempt to answer Calguys questions as refers to one paticular site running 1.2.3 that has the problem:
Is this a new install? no it's an upgrade from a working 1.2
Did this work before? yes
What version of CMSms? 1.2.3
Have you installed any new modules? it has several modules installed and running but all were installed before it was upgraded and while it still worked
Have you made any changes to CMSms? no
Have you verified you meet all the requirements of CMSms? not sure what you're getting at but it was installed as normal and upgraded as normal. I use Cute FTP Pro 3 to FTP files to the server which is running a LAMP configuration and PHP5 and MySQL 5. If you need phpinfo let me know and I'll email the link privately.
I hope this will help sort out a VERY annoying bug.
Cheers.