try catch...............

Question

 I added a try catch in my code to raise error

 

but there shows error--->The name ex doesnot exist in the corrent contest

 

I also added a namespace--->using System.Runtime.Remoting.Contexts;

 

Still ex shows red in clr...How can I fix it? 

 

try

{

//line of code 

} 

catch (Exception exc)

{

ex.errlog(exc, HttpContext.Current.Request.URL.ToString());

}