Sharepoint Web Part sometimes causing left hand navigation menu to be hidden

where does it happen is it happening in all browsers or just some particular browsers.
do you have any java script in your master pages.
try it in your own machine.
clear your cache and try again and see if you can reproduce the problem

Hi,
what is this web part doing?
Perhaps the web part does not create valid html (eg missing closing tags).
If possible post the html output.
Thanks.
Rainer

Thanks for the feedback and sorry for the slow response. It turns out that the masterpage and my webpart are both importing the same jquery library.

<script type="text/javascript" src="/_catalogs/masterpage/js/jquery/jquery-1.4.2.min.js"></script>

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This is causing my jquery selector to fail when the page loads. I don't understand why this wouldn't throw an error everytime instead of only sometimes.

 $(function() {
 $("input[id$='usernameTxtBx']").autocomplete({
            source: function (request, response){
                $.ajax({
                type: 'POST',
                contentType: 'application/json; charset=utf-8', 
                url: '~/_layouts/UsernameAutoComplete.asmx/GetUsernames',
                data: "{ 'partialUsername': '" + request.term + "', 'maxResults': '10' }",
                dataFilter: function(data){return data;},
                success: function(data) {
                    response($.map(data.d, function (item){
                        return{
                            label: item,
                            value: item
                        }
                    }))
                }
            });
        },
        minLength: 1
        });
    });

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I know I can just take the line to import the jquery library out of my webpart, but if the web part were to get loaded on a page that did not import the library, then the webpart would also fail. What would be an appropriate way to handle this?