OK I have discovered that the databases have been changed somehow. If I try to add a page for example I get a 'does not allow nulls error on TabOrder', table 'XXXXXXXXXXXXXXX.dbo.Tabs'; column does not allow nulls', so I went into the database and changed this table to allow nulls. After that I got an error for the same thing on another table, did the same thing by changing that to allow nulls and now I can add a page to that site. Once I had that page I tried to add a module to it, got the nulls error, changed IsDeleted in TabModule to allow nulls and now I can add a module.

So it looks like all the sites have had some weird thing happen to their databases and I now have all these sites with random disallow null values set where it should allow a null. Is there a way I can set all these back to how they should be with an SQL script? I assume that because I don't know what tables have been altered that running upgrades will fail.

That's what worries me, the only way this could happen is if someone other than me has altered either the code or the databases on a large number of my websites. I just don't understand how this could have occurred in the first place unless it was malicious.

Thanks Hans, I have asked the host to check this out as an option.

I have done some A-B comparisons of a fresh install and looks like the columns are set as they should be so they haven't been changed. Also as a test i took one of the sites and moved it to another server environment, created a new database and restored it from a backup. Got the same insert errors on that copy of the site.

Totally confused now.