Rebuild Permissions Not Working

The top of every page on my site says:

The content access permissions need to be rebuilt. Please visit this page.

Every time I rebuild the permissions, it gives an error:

An error has occurred.
Please continue to the error page
An HTTP error 404 occurred. /batch?id=41&op=do

with the id=41 number increasing each time I try (started with id=1)

continuing to the "error page" gives me this:

# The content access permissions have not been properly rebuilt.
# The content access permissions need to be rebuilt.

I checked the log, and there are several 404 errors looking for a page called "406.shtml" so this makes me feel like it's returning a 406 Not Acceptable error, but I don't know how to fix that.

Also, after checking the MySQL database, the node_access table is an empty set. I've been manually resetting the table with this:

insert into node_access values (0,0,'all',1,0,0);

but it still says the content access permissions need to be rebuilt, and none of my access restrictions are in place for the content type "pages." I'm stuck! I have disabled, uninstalled, and deleted all modules I installed today(content access, nodeaccess, ubercart, ecommerce, and a few others), which is when I started receiving this message, and it won't go away! Any help?

Also, I do not have content access or nodeaccess modules installed.

EDIT: I'm running drupal 6.9