issue with linking to menus

I am using J1.6 with CB1.4 and have reinstalled both but still face the same issue.
When attempting to link article content directly to a menu item all of the articles display correctly in article manager but several do not display in the drop down menu when in the menu management screen after selecting use single article.
The system was working fine up until around item 30 but has suddenly stopped working and still is the same after reinstallation.

Any thoughts on what could be causing this and steps to resolve the issue.

Many thanks.

Graeme

Never heard of this one before - as I see it its 100% a joomla issue and I cannot see it CB related in any way - unless I missed something.

Which version of Joomla - exact version please?
Try upgrading to latest Joomla 1.6.4.

Thanks for the reply.
The version used is 1.63.
How would you recommend upgrading to 1.64 to check if this resolves the issue?
If this does not resolve the issue is there anything else you would suggest that may be worth looking at?

Thanks

Graeme

upgrading to Joomla 1.6.4 is needed - yes.