Dia stopped working on Mac OSX 10.11.3 (El Capitan): when trying to launch, xterm launches.

[Katrin Schweitzer <Katrin Schweitzer ims uni-stuttgart de>]

Dear list,

I just recently started using Dia  on Mac OSX 10.11.3 and it seemed to work fine.

However, suddenly it won't start any more. 

The problem started, when I minimized Dia and couldn't get the windows back. I force-quit it and trie to restart. Then, I received an error message that seems to be typical with many Mac applications "The application Dia.app is not open anymore" and that supposedly is fixed by a reboot. After rebooting, Dia won't start either.

When I try to open the application now, xterm launches. Nothing else happens.

Can anyone kindly point me to what to do (or where to research further)?

I am creating a talk with a bit of time pressure and would reeeeally like to be able to access my Dia graphs... :-)

Thank you for your help!

Kati