403 Error when creating or edit an event

Hello,
after Update from Joomla 2.5 to 3.4 and update to JEvents 3.4.4 we can not edit events in the frontend and backend, too (403 "You are not authorised to view this resource/perform this task.". I prooved it as autorisied user and also deactivated authorised user mode as Joomla super user.

PHP Version : 5.4.45-0+deb7u2

MySQL Version : 5.5.46-0+deb7u1

Fix jQuery? : Yes

Load JEvents Bootstrap CSS? : Yes

Load JEvents Bootstrap JS? : Yes

Max Input Vars ? : 1000

Club code set? : No  

Joomla : 3.4.8

component_com_jevents : 3.2.21

component_com_jce : 2.5.12

module_mod_jevents_cal : 3.2.21

module_mod_jevents_custom : 3.2.21

module_mod_jevents_filter : 3.2.21

module_mod_jevents_latest : 3.2.21

module_mod_jevents_legend : 3.2.21

module_mod_jevents_switchview : 3.2.21

plugin_content_jevents : 3.2.21

plugin_search_eventsearch : 3.2.21 (not enabled)

What could be the reason for this problem?

Best regards, Astrid