Problem with #connector_text_filter

The filter in the header does not work. Not even an empty grid is displayed.

<script type="text/javascript">
    function printLog(text) {
		document.getElementById("ta").innerHTML = text + document.getElementById("ta").innerHTML;
		document.getElementById("ta").scrollTop = 0;
	function gridXLS() {
		printLog("загрузка данных ...<br>");
	function gridXLE() {
		printLog("данные загружены<br>");
        //---grid initialization
        mygrid = new dhtmlXGridObject('mygrid_container');
		mygrid.attachEvent("onXLS", gridXLS);
		mygrid.attachEvent("onXLE", gridXLE);
        //---dataProcessor initialization
	    var mydp = new dataProcessor ("db.php");  specify a connector file

Without this line
the grid is displayed.

What am I doing wrong?

in version 2.6 build 100722 this all works fine

Unfortunately, I was not able to reproduce your issue locally.
the following snippet seems to work correctly:
If the problem still occurs for you could you please, provide a simplified complete demo, where the problem could be reconstructed.
Here you can find a tutorial about creating a complete demo:

I have prepared an archive with all the files for you. My data is stored in a MySQL database, there is a demo dump in the (185.0 KB)

Hello. Managed to reproduce my issue locally?

My apologies for the delay with the reply.

In your using dhtmlxGrid package sources there are no connector filters.
Unfortunately, All I can suggest, in this situation, is to update your dhtmlx package, as the using 3.6 build is not supported anymore and it is hard to find any suitable solution, that will work for sure.
Otherwise, you may try to use your own custom filtration based on the onFilterSatrt event:

Thanks. Can you advise which version of dhtmlxGrid package should I use to be able to output data from a database with built - in filters and the ability to customize cells ?

In your case you may try include the following extension from the dhtmlxConnector on your page:

It may help. Otherwise, it should work for sure with the dhtmlxSuite 5.2.

Can you tell me where can I download version 5.2?

As we are not selling it anymore it is not easy to find it.
Here is a link to download the 5.2 GPL build: