Hey there marmotte73. Thanks for reaching out, and apologies to hear of your inconvenience so far. It looks like this error message is being generated by the theme rather than the calendar; what is the code on line 5 in the php file referenced? Mind dropping it into a pastie.org link and sharing here?
Also, if you haven’t done so already, it’d probably be worth starting a similar thread on the DynamicPress/Gantry forum so their devs can take a look as well. Let me know about the above and we’ll do what we can.