Assuming you are using "onblur" event to call the javascript,
http://www.w3schools.com/jsref/event_onblur.asp
1. Check in the status bar if you are getting any script error, if so check the script you are calling on "onblur" event of textbox.
2. If you dont find any script error, check with something simple script to see if the javascript is working, for e.g.
onblur='javascript: alert("test");' if you are receiving an alert message, that means the browser and javascript are working fine. You need to debug the script you are calling on "onblur" event of textbox.
3. If you still not able to find the error, post the script you are calling on the onblur event.
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