[TYPO3] Flexform problem: all languages shown at once

[Pieter]

Hello all,

I'm running into troubles with the flexform of the newloginbox.  The 
backend shows the flexfrom 4 times underneath each other (one time for 
each language on the website: DEF EN FR DE).  If I click one of the tabs 
of the upper flexform (for example "Welcome"), the lowest flexform of 
the 4 actually jumps to that page.

If I change something and save I get a series of errors.  Now, I can't 
edit the content element at all any more.  Instead I get some error 
messages:

Warning: array_unique(): The argument should be an array in 
<full_path>/typo3_src-4.0/t3lib/class.t3lib_tceforms.php on line 2075

Warning: in_array(): Wrong datatype for second argument in 
<full_path>/typo3_src-4.0/t3lib/class.t3lib_tceforms.php on line 2086

Fatal error: Only variables can be passed by reference in 
<full_path>/typo3_src-4.0/t3lib/class.t3lib_tceforms.php on line 2087

I did a database compare, cleaned the cache, searched Typo3.org for 
"array_unique", searched the newsgroups but nobody seems to have this 
problem.

Configuration:
Typo3 4.0
newloginbox 2.2.11
"Modern template building" website
sr_feuser_register 2.3.3

What is happening on this site?

Pieter