TYPO3 Core

I'm not abled to add more subpages to my Homepage, the arrows for selecting
the location are missing. (http://holthausen-biene.dlrg.de). There are no
problems to add pages on 2nd level, but 1st level pages are not possible (1st
level do NOT mean root-level, there is only one page possible). Up to now
there is no other user reporting this problem and on another account it works with the same system (tried it myself).
I have added pages often, but suddently it does not work anymore. Maybe a
reason is the number of subpages, but I do not know about a limit?
I already contacted the administration of our own (DLRG-)servers, they orderd
me to contact you.
If you need more informations or screenshots please contact me.
I'm sorry for my bad english,

I tried to find the missing element with firefox firebug. It is this element missing for pages on the level I want to create.
<a onmouseout="changeImg('mImgSubpage1',1);" onmouseover="changeImg('mImgSubpage1',0);" onclick="window.location.href='../typo3conf/ext/templavoila/mod1/index.php?cmd=crPage&positionPid=83189';" href="#">

I'm not 100% sure about the php/Typo3 version, but our administrators said it's the newest one!
(issue imported from #M10637)