Hello Sebastian Herth,

Sorry for late reply to this,
Can you try consult with your webhosting provider and see how it goes? Keep us updated then after you get back from your Webhosting.

Internal Server Error



The server encountered an internal error or misconfiguration and was unable to complete your request.



Please contact the server administrator, [no address given] and inform them of the time the error occurred, and anything you might have done that may have caused the error.



More information about this error may be available in the server error log.



Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I can see only this in log file
2014-06-25T18:38:02+00:00 INFO controller Holding edit ID com_menus.edit.item.3778 Array ( [0] => 3778 )

It was an server time out error. After several attempts to install the component via Joomal I deinstalled the component (extension manager) and deleted all database entries via PHPMyAdmin and then did a fresh installation.
Now it works.
You may close the thread. Thanks for your attention.

Hello Sebastian Herth,

You're welcome, glad to heard your issues resolved.