1) Please check error log for possible fatal errors. Make sure you are calling $g->get_dropdown() function after the object creation $g=new jqgrid(); Error log of apache will show exact reason of blank page.

2) Most likely, the upload_dir path does not exist and php has not enough rights to create folder.

3) You can use mysqli extension using database layer. See this faq.

Q) How to use mysqli extension?

Here is the config settings.

$db_conf = array();
$db_conf["type"] = "mysqli";
$db_conf["server"] = "localhost"; // or you mysql ip
$db_conf["user"] = "root"; // username
$db_conf["password"] = "test"; // password
$db_conf["database"] = "griddemo"; // database

// include and create object
$base_path = strstr(realpath("."),"demos",true)."lib/";
include($base_path."inc/jqgrid_dist.php");
$g = new jqgrid($db_conf);

I fixed the three problems with your solutions! Thank you very much!

Q2

How to find out or debug what is wrong.
I can't get it to work.
I allways get the messages "Unable to move to desired folder /Image.
Directory excist and has 777 permission

This message is pushed when move_uploaded_file function returns FALSE inside lib (jqgrid_dist.php)

By documentation:
If filename is not a valid upload file, then no action will occur, and move_uploaded_file() will return FALSE.
If filename is a valid upload file, but cannot be moved for some reason, no action will occur, and move_uploaded_file() will return FALSE. Additionally, a warning will be issued.

To get the warning error:
Edit jqgrid_dist.php and search for move_uploaded_file and remove @ sign.

if ( @move_uploaded_file($tmp_name, "$uploads_dir/$name") )
{
$msg = "$uploads_dir/$name";
}
else
$error = "Unable to move to desired folder $uploads_dir/$name";

how to fix this issue sir