Subprojects are consistently "offline"

[CoffeeQuest]

I've been using subprojects but I've run into something weird.
Whenever I create a new subproject, e.g. by making some tracks in a folder, right-clicking on the folder and choosing "move tracks to new sub-project", Reaper will make them into a subproject, but it keeps being "offline". When I double click to enter the subproject I get into the item properties instead. I try to "choose new file" and direct it to the recently created subproject, but it doesn't work.

The subproject rpp-files are automatically places in the media folder for my project. I don't know how to proceed. Has anybody has any similar problem with sub-projects? And better yet, know how to fix it?