[TYPO3-calendar] FE-Editing

[Josef]

Hello list,

I'm trying so up FE-Editing.
- Static Template added,
- Frontend Editing is enabled in Constant Editor
- Frontend user/Frontend Usergroups are specified
- Rights are assigned

The "create event"-symbol appears. But when clicking on it, I get a "white 
screen". Nothing is shown.
(TYPO 3 7.4.0 and 7.5.0, cal 1.10.0, php 5.5.28)

In my old installations there are no problems with FE-Editing.
Is there something new to setup? Bug?

Thanks in advance.

Regards,

Josef