str_get_html is not loading a valid html string

I receive an html string using curl:

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$html_string = curl_exec($ch);

When I echo it I see a perfectly good html as I require for my parsing needs. But, When trying to send this string to HTML DOM PARSER method str_get_html($html_string), It would not upload it (returns false from the method invocation).

I tried saving it to file and opening with file_get_html on the file, but the same thing occurs.

What can be the cause of this? As I said, the html looks perfectly fine when I echo it.

Thanks a lot.

The code itself:

$html = file_get_html("http://www.bgu.co.il/tremp.aspx");
$v = $html->find('input[id=__VIEWSTATE]');
$viewState = $v[0]->attr['value'];
$e = $html->find('input=[id=__EVENTVALIDATION]');
$event = $e[0]->attr['value'];

$html->clear(); 
unset($html);

$body = " A_STRING_THAT_CONTAINS_SOME_DATA " 

$ch = curl_init("http://www.bgu.co.il/tremp.aspx");
curl_setopt($ch, CURLOPT_POSTFIELDS, $body);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$html_string = curl_exec($ch);

$file_handle = fopen("file.txt", "w");
fwrite($file_handle, $html_string);
fclose($file_handle);

curl_close($ch);

$html = str_get_html($html_string);