Mac OS X 10.0: Cannot Have Two Open Versions of Microsoft Internet Explorer
You cannot use Internet Explorer 5.1 for Mac OS X at the same time as Internet Explorer 4.x or 5.0x in Classic.
Symptom
A second version of Internet Explorer will not open when a different version is already open.
Solution
Quit Internet Explorer before attempting to open a different version.
Published Date: Feb 17, 2012
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