getelementbyid style doesn't work in IE

[Panjabel]

i have an image with assigned id="loading"

when i select the menu from select menu, the image is getting visible

when the operation is done, the image doesn't get invisible

in firefox it does, but in IE it doesn't

any suggestion please ?

need urgently

[Panjabel]

ajaxscripts.js

.........................

function country()
{
if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0)
{
// some code
xmlHttp.onreadystatechange = country_get;
xmlHttp.send(null);
}
}
function country_get()
{
if (xmlHttp.readyState == 4)
{
if (xmlHttp.status == 200)
{
raspuns = xmlHttp.responseText;
// some code
document.getElementById('loading_country').style.visibility='hidden';
}
else
{
alert("Problem: " +xmlHttp.statusText);
}
}
}

.....................

this is index.php

.....................

<label id="continent">
<select name="continents" id="continents" onChange="continent(); document.getElementById('loading_country').style.visibility='visible'">
<option value="Any Continent">Any Continent</option>
<option value="Africa">Africa</option>
<option value="Asia">Asia</option>
</select>
</label>

....................

when i change the continent for the second time, the image id="loading_country" doesn't get back invisible in IE