IE9 stopped working with Selenium C# -

i new selenium, using following code snippet automate menu items[ajax].

ijavascriptexecutor executor; executor = (ijavascriptexecutor)driver;   executor.executescript("return $(\"a:contains('" + category + "')\").mouseover();"); executor.executescript("return $(\"a:contains('" + subcategory + "')\").click();"); 

on mouse-over submenu opened. getting popup message, ie stopped working @ times. how rid of behaviour.