Can you explain the problem in more detail?
I assume that before you did the recent upgrade, you used MediaWiki 1.5 or newer. If so, then I have the following questions:
When you look at a page, the page table inside th DB is used to get a revision number for that page. Next the revision table is queried for exactly this revision and in this process an old_id is obtained. Finally this value is used to get the according text from the table text.
So do you have a corrupted revision table (which does not point to an existing entry in the text table)?
Or are the entries in the text table actually present (old_id does exist), but the according text is empty? In this case: Is it possible that a user has just deleted the text through MediaWiki and saved an epty page instead? IIrc you can see the size differences when you compare the according fields in the revision table.