OK, the path I'm following is to upgrade to 522, then to 541.
The plan was to install some modules at this stage (522) which of course I can't do as I can't even browse to the page.
The error can't be safely ignored but then again, I don't HAVE to install modules at this stage. It's just that Catalook 6.0.8 has been tested up to 5.3.1 so I wanted to put it back in now.
I had to remove it from 4.9.5 prior to upgrade as having the db objects present was causing issues with upgrading DNN itself as. The version in DNN 4.x is their 5.8.1. Won't work in any 5.x DNN install and 6.0.8 isn't backward compatible to DNN 4.x. The only option was script out content, uninstall, etc.
Anyway, that's all too much info. Bottom line is I can't get to Hosts | Module definitions as no page whatever comes up.
I can just do the 2nd stage and upgrade to 541 but will this fix matters or not?