[TYPO3-english] flexform sections gives error after 45 section entries

[Domi]

Hello,

I wrote a FCE with flux/fed and stumble over the problem, that after 45 
entries of section objects I get a error message while saving:

Validating the security token of this form has failed. Please reload the 
form and submit it again.

Before the 45 entries the flexform FCE worked fine. From now on nothing 
could get edited, deleted and so on, the flexform FCE is simply uneditable.

Is there a flexform configuration which limits the count of section 
entries for TYPO3 content elements?

Thanks for any hint,

Dominic