Ahh that, its the file this is very well known maya behaviour*. You can get around this problem by first opening a clean maya and then opening the file in question. So avoid opening things into maya by doubleckiking files in the operating systemds file browsers, and you will sidestep this issue.
See maya files are quite malleable, whereas maya gui is allways, not. There are several reasons why youd omit the definitions. However the init of the panels will crap up (the panels are mead first THEN it cheks for the existence of the cameras).
You can simply just open the file save it and its should be fixed for the next time you do this.**
- Its been there for about as far as i remeber maya (from maya 1 maybe?), we all learned to work around the problem so well it never manifests itself. To be totally honest tough theres a VERY easy fix for this but its bit hairy. So unless your a programmer dont apply for this solution.
In fact a lot of users rely on this behaviour.
** dont EVER touch or reuse use the default cameras in your scenes. Allways create the sue cams yourself. The 4 defaults are supposed be purely for investigative purposes only.