When upgrading from 4.3.1 to 4.3.2 I encountered the above error. A few posts in the DNN Forums suggested there were problems with the portals defined. In my case, I had one portal defined with id of zero (0) yet there was also a portal id one (1) called “My Website” with most other columns null. I started the 4.x journey with 4.0.2 and checking there I found only one row in Portals. So....perhaps the upgrade to 4.3.1 did something? Anyway, I had just tried my cookbook approach to upgrading posted about here so I simply deleted the database, recopied, fixed the aliases then deleted the spurious row. When I first hit the site it ran through the upgrade perfectly then I clicked the link at the bottom of the upgrade report page and was “in like Flynn”.