TAB control is hidden on IE7

I've found a strange problem that occured only on IE7

I have a wep page (MAINPAGE) that containt an IFRAME. This page is use to put our menu. The content of our website is display inside the iframe. So here is the problem. I have made some page with the new tab control. I will call those page PAGE1 and PAGE2. So if i put a hyperlink in PAGE1 to open PAGE2 everything is working fine. In our menu i use this:

"window.frames('fraMain').location.href = '" & row("URL").ToString & "';"

This is is code for the event onclick in our menu. So when i use this code to open either PAGE1 or PAGE2 the tab control is not displayed. I've got a javascript error "unspecified error" and if i look at the source code this is what the tab control looks like:

<div id="ctl00_Contenu_TABGENERAL" class="ajax__tab_Orchestra"style="visibility:hidden;">

So there is avisibility:hidden add to the code. This only occured on IE7 and when my pages are called using this line of code "window.frames('fraMain').location.href = '" & row("URL").ToString & "';".

We've been using this line of code for years and never have any problem with any other pages that don't containt the TAB control.

Any idea ?

I've made some other test and i notice that the problem only occured the first time i open the page with our menu. So if i click on our menu to open the page the Tab control is not displayed. Then if i click again the tab control work just fine. I don't have this problem with Firefox.