We recently upgraded our servers to 11.20 SR3 from 10 SR 3 and still have the 10 SR3 IE plugin deployed to our clients with out any reported issues. We do know that there is an issue with using the 11.20 IE plugin to access the down level 10 SR 3 environment.
Hey steve yesterday i can solve this problem, well maybe it is temporally but i just rename the "opendoc_fix" file to "opendoc" i found it here "C:\Program Files\QlikView\Server\QlikViewClients\QlikViewPlugin" and the old one i just renamed it opendocold, it works for me, good luck !!!