fixed,
the error was caused by another plugin. It was “Counterize”.
@cais: Thanks for your reply, bug is reported.
Solution is here:
http://www.kriesi.at/support/topic/choices-nextgen-issue/
it doesn’t fix the cause of the problem but cures the symtoms. I don`t receive any error-messages.
Nextgen Verson 2.0.33, WordPress 3.6.1
regards, Andre