[TYPO3-ttnews] EXT:news, tx_news, Error: Create or Editing a news-record in the backend

[Christian Koeroesy]

Hello,
i'm using  the fine tx_news (v2.1) for several weeks without any 
problems on a multilanguage TYPO3 insallation (de/en):
TYPO3 6.0.5 (now after a major upgrade 6.1.1), PHP 5.4.16, Linux
Example Page:
http://www.hpi-ag.com/investor-relations/unternehmensnachrichten/

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Since last weeks i can't edit or create a news record successfully.
In the edit mode the title and date fields are always empty now. The 
teaser and text fields(RTE) are filled correctly. Moreover i can't 
create a relation in the relations tab. I klick on "Create new" -> a new 
relation box appears, but it does not open any more.

All existing news records and categories are listed correctly in the 
Backend in list mode.

What i have checked/done so far:
- updatet TYPO3 to 6.1.1
- truncated cf_* tables
- reinstalled tx_news
- There are no errors listed in the Backend log
- i have no access to other logs so far
- i have not made any changes to the backend

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Did someone heard of that problem or could give me a hint how to proceed?

I would really appreciate any help

Best Regards
Chris