When I started up my development machine (mid-2011 iMac, Yosemite 10.10.3) I noticed that my debug configuration had disappeared: when I had last used this machine three days ago there was no problem with it.
Opening the Edit Configurations dialog, I saw that the debug configuration was replaced by a question mark and the word Unknown.
Clicking the triangle before it showed the former configuration as the word Debug with a shortcut icon adorned with little red 'error' cross (see screen capture). In the right panel it said:
Broken configuration due to unavailable plugin or invalid configuration data.
When I clicked on the word Unknown, this was replaced by the deeply puzzling
Press the + button to create a new Configuration which cannot be loaded due to some reasons based on default settings
which made me laugh, because it's sheer absurdity reminded me of Monty Python's Flying Circus - or the nebulous "General Failure" errors that Windows 95 and 98 produced.
Because I had seen one other application generate an error during start-up, I closed and re-opened Intellij, and the debug configuration was restored.
I'm posting this mostly because the error message really made me wonder what caused this situation: I'm especially curious to what Intellij considers some reasons - and I'd also love to know why on earth it would recommend to create a Configuration which cannot be loaded ?