Error on page submit

Please help with the following.

I have one index.php file that contains a form. This form is submitted to index.php where I get the variables sent by $_post.
The problem is that after I submit the page, it returns blank. It contains no header redirects, and all include files exists and working great.
I have tested this application on three servers.
On two, that have prety much the same structure, this works great, but on one it returns the blanc page.

Settings for Server 1 (works great)
doc_root: /home/user/public_html
SCRIPT_FILENAME: /home/user/public_html/blabla/index.php

Settings for Server 2 (works great)
doc_root: /home/anotheruser/public_html
SCRIPT_FILENAME: /home/anotheruser/public_html/blabla2/index.php

Settings for Server 3 (not working)
doc_root: /e3
SCRIPT_FILENAME: /e3/folder/earth/moon/index.php

The index.php includes 3 files, 2 classes and one settings. There is no error on this.
Please consider that I am not a beginner, and all the include files works great, and that are running on some other websites and are working great.
I have one .htaccess file that changes the maximum post size, and upload size.
The 3rd server belongs to a university, and I don’t know their settings and I can’t find them. But what could be wrong? Why the blank page?

Thx in advance.

The blank page usually indicates a fatal PHP error occurred but the error reporting level is not set to display the error. Change the error reporting level or check the error_log file.

Is the display errors enabled for this, you might be able to debug this.