The JQuery UI 1.10 Upgrade Guide indicates
JQuery UI 1.10 removed support for IE6
The IE6 usage has dropped to a, enough point, jQuery UI no longer finds it necessary to support. As of 1.10.0, some portions of jQuery UI may isn't work properly in IE6. If you need to continue to support IE6, use the latest JQuery UI 1.9 release.
Original: http://jqueryui.com/upgrade-guide/1.10/#removed-support-for-ie6
JQuery UI 1.11 Discontinued IE7 Support
As of this release we is no longer accepting bug reports for IE7 issues. We have also removed IE7 from our testing infrastructure. The IE7 workarounds is still present in the code, but we'll remove them for jQuery UI 1.12.
http://jqueryui.com/upgrade-guide/1.11/#discontinued-ie7-support
That is, only jquery UI 1.9 and the following versions are supported IE6
JQuery UI 1.10 No longer supports Ie6,jquery UI 1.11 no longer supports IE7