Hello are you a dev?
When retrieving data from the db, you are getting the array keys as if they were defined as constants, too bad you didn't posted the error, or db structure, but it may be the following kind of assignments:
if(!empty($row_u[objekt1]))$h_neu = 2;
should be
if(!empty($row_u['objekt1']))$h_neu = 2;
I can not run it otherwise I will let you know what's wrong in just a few minutes.
Edit: Hello, the problem is in the captcha, it seems that it requires a table/database which expects a row that couldn't be found. If you accept my bid I will spot the issue and find a solution within a few minutes.