I receive the same error. I recently completed a series of upgrades, 4.0.1 -> 4.3.1 -> 4.3.3. All of them completed with no errors. When I try to create a new portal, child or parent, I receive "Error creating Portal."

My existing portal has the path, www.mysite.com/site. I tried to add a child portal with the alias, www.mysite.com/site/child using the default home directory "Portals/[PortalID]" and it does not work. I tried specifying a home directory relative to the host directory and it did not work either.

I just found the great post by laurencepostgate on this thread:

http://dotnetnuke.com/tabid/795/forumid/107/threadid/45127/threadpage/1/scope/posts/Default.aspx

There's some good substance in laurencepostgate's post, helps with troubleshooting...