ASP.NET Javascript: window.open won't work twice

I have an aspx page with a button. When the user clicks that button, the following javascript opens a new browser window (in this case, 'Reasons.aspx'). Works great. Here's the function for that part:

function ShowPanel(url)
{
var width = 750;
var height = 600;
var left = (screen.width - width) / 2;
var top = (screen.height - height) / 2;
var params = 'width=' + width + ', height=' + height;
params += ', top=' + top + ', left=' + left;
params += ', toolbar=no';
params += ', menubar=no';
params += ', resizable=yes';
params += ', directories=no';
params += ', scrollbars=no';
params += ', status=no';
params += ', location=no';
newwin = window.open(url + '?LetterNumber=1&ReasonType=3', 'd', params); //<--- Change This (LetterNumber) When Copying!
if (window.focus) 
    {
    newwin.focus() 
    }
return false;
}

Now here's where it gets funky. When this window pops up, there are some controls. One of which is a button, which triggers almost identical code to popup a third window (in this case, ReasonCodes.aspx). Only it won't work. Here's the code for that:

function fGetReasons(url)
{
var width = 750;
var height = 600;
var left = (screen.width - width) / 2;
var top = (screen.height - height) / 2;
var params = 'width=' + width + ', height=' + height;
params += ', top=' + top + ', left=' + left;
params += ', toolbar=no';
params += ', menubar=no';
params += ', resizable=yes';
params += ', directories=no';
params += ', scrollbars=no';
params += ', status=no';
params += ', location=no';
newwin = window.open(url, 'd', params); //<--- Change This (LetterNumber) When Copying!
if (window.focus) 
    {
    newwin.focus() 
    }
return false;
}

I've set breakpoints on the javascript. It does execute. Here's what's weird -- The above javascript executes, only I don't get a new window with ReasonCodes.aspx. However, I set a breakpoint in the page_load of ReasonCodes.aspx and all of it executes. So the javascript executes, the code-behind page_load of the third page executes, but I don't get a third page.

Instead, the second window (Reasons.aspx) refreshes. It's like my third window is somehow 'hidden'.

Can anybody tell me what's going on, or what am I missing?

Thanks,

Jason

PS -- I know 3 windows sounds like a lot, and it's not by choice. There's a business need here (this is a local intranet application) and I have to abide by the specs. Thanks.