I tried with JMeter 2.10 and doesn't work either. I used Fiddler <http://fiddler2.com/home> and could capture the traffic, looking at the requests captured I see that, as you say, the single-quotes are part of the charset name, almost all web requests have in the field content text/html;charset='UTF-8'.
Is this a problem of the app? should it be modified in order to remove the single-quotes form the charset name? I think I will use a 30 days trial version of an app called Test Studio<http://www.telerik.com/automated-testing-tools/>, in this app I can import the traffic captured with fiddler directly, while for exporting the traffic in a format that jmeter recognizes, i'll have to make this fiddler extension<http://www.perftesting.co.uk/creating-jmeter-test-plans-with-fiddler/2013/03/01/>, and I don't have too much time for this. Thanks.
