datePickerProbem with Ajax

I have a problem with datepicker and ajax.

I have a form with some datepicker, and some of them are in a part of form that is reloaded with ajax.

When I reload this part, the datepickers reloaded works properly, while the datepickers not reloaded stop to work.

I have noticed that reloading html containing datepickers changes the last part of the body of my page, and add more lines like that:

<div id="ui-datepicker-div" class="ui-datepicker ui-widget ui-widget-content ui-helper-clearfix ui-corner-all ui-helper-hidden-accessible"></div>

I guess that maybe is correlated.