Thanks Sympmarc for quick response,
Wel,i think i need to explain bit more about my current scenarios,
Actually i have stored following JS Files in layouts/ABC/Scripts folder.
1.Dispform.js (MyCustom JS)
2. JQuery JS
3.SPService JS
i call Jquery & SP Service methods from DispForm.js
For Reader : i got exception while accessing SPService methods from DispForm.js. if i commenting SPService methods , JQuery method works from DispForm.js
For SCA : It just works
My Asslumption here is, if reader doesn't have access, then JQuery also should not work. but its getting called from DispForm.js
Hope i have explained better than before :)
Thanks
Sundar