Table don't load in IE6,7 and in some cases in IE8

Marios

Hello,
I have the next table: http://datatexample.mywebcommunity.org/table.php
the problem is that only appears the message Prossesing and the table don't get the JSON from the php file.
I made test with firebug and developer tools from IE8 and these don't show any errors,the JSON is valid in jsonlint.com
searching in the forum I find this post: http://datatables.net/forums/discussion/7699/serverside-processing-doesnt-work-in-ie8/p1 , is the most similar to my case but I don't find yet the problem.
I have ommited the pipelining function and the HTTP variables but is the same result.
Can you give me some advise?
Thanks
Edit: When I make a search in IE send this error: "json.aaData is null" when pipelining is active.

Marios

The last issue is now corrected using the POST method.

Now I have a problem of misalignment in header columns when sScrollY is applied.
I have changed in the css the dataTables_wrapper class position from relative to absolute and this function in the javascript.

[code]function gridRenderer(oObj) {
var column = oObj.iDataColumn;
var columnAnchor = oObj.oSettings.aoColumns[column].mDataProp;

var content = oObj.aData[columnAnchor];

if (content == "null" || content == null) {
content = "";
}
var result = ""
+ content + "";

return result;
}[/code]

when sScrollY is not active the headers are aligned without any problems but I need the Scroll for make the headers always visible.
Best regards