this question may look a little like these: Magento Grid Container Block not loading grid Grid doesn't appear in custom admin module in Magento but it isn't the same issue, I believe.
I'm not the admin in this magento store, I only do some support/bugfix work on it. Server had Magento v1.3 installed, and there was a group of custom modules (I don't even know what were they for :P) written for it. Everything worked fine until someone updated Magento to v1.5. Every module had a grid with some data in it.
After updating, the grids stopped showing up, so pages where there were grids, are now blank, only the rest of admin panel (menu, etc.).
I guess modules were written for 1.3 and there is some common cause for them to disappear after update. I don't think that any core files were edited. Did you ever encounter such problem? If yes, can you give me any hint about how to bite this problem?
Cheers, Maćko