Iframes and IE and cross-domain

we have a page hosted on our website that has a table - one cell has a iframe in it.

<TABLE><TR><TD valign="top">
<iframe src="appaend.cfm" width="400" height="600" frameborder="0" scrolling="no">
</iframe>
</TD><TD valign="top">
<iframe src="framesource.cfm" width="1000" height="600" frameborder="0" scrolling="no"></iframe>

</TD></TR></TABLE>

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The code for the framesource is a form that submits to another website (one that a partner is hosting).    

<CFFORM ACTION="theotherdomain.com/file.asp" method="post">
<CFOUTPUT>
<input type="hidden" name="sendto" value="#tempid#">
</CFOUTPUT>
<input type="submit" name="go" value="Access App">
</CFFORM>

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In all browsers except for IE, the user (who is already authenticated on our website) is automatically logged in on their end using the information that we send in the form above.  In IE, it tells the user to login.      The form process works outside of the iframe in IE so it isn't a tech issue from that standpoint.    Anyone have a solution for this?    I am open to pretty much anything at this point.   Basically we are hosting the "help" side of the app and they are hosting the app.    I was thinking a sticky pop-up but this was a better idea at the time but if it doesn't work in IE...