Exception handling in Asynchronous call

Errors are often returned by the web service in a manner that the web service determines. You need to look at the documentation of the web service to know how to get the errors that the web service is reporting.

Ya i have used multiple catch blocks in web service. But not able to catch the error. i want to show some message based on the exception type catched. Also the exception is occuring during the asynchronous call

Do you know if the exception is occuring during the asynchronous call or after the call (in other words, the web service is issuing the error)? If it is happening after the call then I don't understand how a catch would catch the error. Also I don't understand "handle in User Interface"; do you need to be able to determine the type of exception and then process various types differently? Why not simply have multiple catch blocks?