Here's a final follow-up

First - thanks for the tip about running the SQL in the portal window - I've never had occassion to use it, but I will now.

The pain continued for me (seemingly random errors, slow response too), so I got a bit more drastic. I did a parallel fresh install of DNN 4.3.1, then scripted out all of the SPs, since I figured my problems were in there somewhere. I ran the script in my original install and things got a lot better. No errors yet and it feels faster.

I still couldn't log in with admin accounts on some portals though, but I realized they were the portals created when the application name was changed (see above). I verified this idea by looking at the aspnet tables, but I fixed it by creating new admin users instead of manually trying to change the application GUID for the users - that seemed like a dangerous thing to me!

I then deleted the old users through the portals, which caused an error because the user and app name combination didn't exist in the aspnet tables. There are a few remnant users in there now, but I don't think it matters - they can't be deleted manually anyway.

I can now login with all my accounts and create child portals

Sorry guys... Happy to hear it has worked... I am noob at this, so...

Okay logged in as Host.
Under host menu selected "SQL".
In Textbox typed "03.02.06.SqlDataProvider"

Is this all I need to do?

Do I need to tick "Script" textbox? Type "GO" before???

Then just click on "Execute"?

Thanks again.

Okay the above couple of posts were not meant to be rhetorical questions... ... but a big thanks to the guys who posted previously. I now understand what was needed.

You take the text/code inside the file called "03.02.06.SqlDataProvider" and copy/paste it into the text filed provided. Then tick the checkbox for "Run as Script", and then click the "Execute" link and within seconds it finishes.

I tried this on 2 websites that had been upgraded from 4.0.3 to 4.3.1 and they can both now create child portals. Just wanted to add this in case it helps others. Thanks again for the posters above. Cheers.