I am having the exact same problem….doesn’t seem like anyone who has ever had this problem has had a solution, or a reason for the error,everything was fine, went to publish a page, and boom, there it is…gonna give it up tonight and reinstall wp in the morning..
I hit this problem — but I managed to solve it.
On looking in the wp-includes folder I noticed a large number of files with zero length. Fortunately I have six installations of WordPress and had already successfully upgraded two of them. I was able to overwrite the zero length files with copies of the correct versions from one of those successful installations.
What caused this to happen I do not know, I blame Fantastico.
I have the same problem. Been a a few days now and I noticed the line mentioned above is: require_wp_db();
I’m upgrading from a previous installation, same db/host/tables. The part that confused me was that installing another copy of WordPress through the hosting tool installed without even a breeze.
Checked out the wp-includes folder as Cornwell suggested, and the filesizes were okay. I took a minute to delete and replace with fresh copies to no avail.
Anyone have any luck with this?