On my website i have several forms and links that use the same method to retrieve the data that should be shown on the website.
Till now all are working great, except one. and it's driving me nuts.

the form:
HTML Code:
<form name="frm_raidroster">
<fieldset class="raid"><legend>Planned raid Monday 05 July 2010</legend>
<a class="dkp_link" href="#" onclick="getloader('modify_for_raid_2010-07-5')">Modify</a><br>
<fieldset><legend>Accepted</legend>  
<table border="1" cellpadding="0" cellspacing="0">
	<tr>
		<td class="raid_call_header">Name</td>
		<td class="raid_call_header">Role</td>
		<td class="raid_call_header">Status</td>
		<td class="raid_call_header">user note:</td>
		<td class="raid_call_header">Admin Note</td>
	</tr>
	<tr>
		<td><input name="membername[]" value="<charname>" type="hidden"><charname></td>
		<td>
		<select name="role[]">
			<option value="Healer">Healer</option>
			<option value="MDPS">M DPS</option>
			<option value="RDPS">R DPS</option>
			<option value="TANK" selected="selected">Tank</option>
			<option value="Unkown">Unknown</option>
		</select>
		</td>
		<td>
		<select name="status[]">
			<option value="ACCEPTED">Accepted</option>
			<option value="QUEUED">Queued</option>
			<option value="CANCELLED">Cancelled</option>
		</select>
		</td>
		<td>
			<input name="user_note[]" value="" type="hidden">
		</td>
		<td>
			<input name="admin_note[]" value="" type="text">
		</td>
	</tr>
	<tr>
	..... more lines same as above 
	</tr>
	</table>
</fieldset>
<input name="raidrosterupdate" value="update" type="hidden">
<input onclick="SaveRaidRoster('saveraidroster')" value="Apply change" type="submit">
</fieldset>
</form>
<div id="raidroster"></div>
<charname> are names from the database

The javascript function used is:
Code:
function SaveRaidRoster(action){
if (window.XMLHttpRequest)
  {
  xmlhttp=new XMLHttpRequest();
  }
else
  {
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
var membername = document.frm_raidroster.elements["membername[]"];
xmlhttp.onreadystatechange=function()
  {
  document.getElementById("raidroster").innerHTML='<img src="ajax-loader.gif" border="0" alt="loader" />';
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("raidroster").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","menuaction.php?action="+action+"|"+membername ,true);
xmlhttp.send();
}
When i debug the script with firebug I see the data being passed to the VAR membername., menuaction.php recieves the data in good order.

The thing that is driving me NUTS is that after the script is done, its fills the address bar of my browser with the form data and returns to the index page.
Where it should result in just showing the data parsed back from menuaction.php. That data is shown while I debug. but after the script leaves the onclick event from SaveRaidRoster('saveraidroster') it goes a-wall.

would love to see someone point me in the right direction.

/Fons