showPrintPreview and "Error: Permission denied to access property 'isc'"

GWT 2.6.1 and SmartClient Version: v9.1p_2014-08-24/LGPL Development Only (built 2014-08-24)

Since upgrading and moving to showPrintPreview, I am getting the following error on all browsers:

Error: Permission denied to access property 'isc'
if (window.parent && window.parent.isc) {

The SGWT application is wrapped in an iframe which is embedded in a Blackboard application:
<iframe src ="gwt/AdminGUI.html?course_id=<%=courseId%>" width="100%" height="950">
<p>Your browser does not support iframes.</p>
</iframe>

Note that the print dialog works on an http:// test Blackboard system but the error is generated when using an https:// test Blackboard system.