Great support from real developers!

Installing of this plugin starts with an initial setup. I got a message about “insufficient permissions” although I was using an account with administration rights.

Contacted WPDeveloper support. They (Loren Ashley) responded very fast. Initial suggestions (disabling plugin’s) didn’t work so I granted them acces to the site. They discovered that the Ultimate Member plugin “admin” role is NOT the same as the standard administrator – and that was the problem.
Not only they act very fast: they really know their stuff. Great work!