Upgrading from vs2005 to 2012 ,Getting

Hi All.

I am upgrading my application from VS2005 to VS2012

when i select Target Framework = Farmework 4.0

I am getting below error. 

0x800a139e - JavaScript runtime error: Sys.InvalidOperationException: A control is already associated with the element.

In VS2005 , i am using ajax extensions 1.0 and telerik controls.

i don't know which is causing the above error.

when i select Target Framework = Farmework 2.0 it is working fine.

Could yout please help to resove the error?

Thank You,

Naga Varma