I'm encountering a problem on a site I'm developing. The sub menu for some page disappeared. I can still link to it but its not showing up in my menu. Is there something in the setting that's causing this?

 

I need a few more details, and maybe a screen shot would help.

Which version of DotNetNuke are you using?
Is this happening with a custom skin?
Which menu are you using?
If you switch the the default Minimal Extropy skin is the navigation correct?

Hi I'm using the DNN Version 05.04.04 (2), not its not happening with a custom skin, even when i use the default Minimal Extropy skin, I wasn't able to view some of the sub-menus. what seems to be working is removing the the sub-menu from under the parent page and then replacing it back under the parent page. I'm just concerned that this will happen again suddenly. 

I have not seen this before.

But, I would recommend upgrading to 5.5.1.