How to avoid "User not found" error using EnsureUser()

Hi,

I am trying to get SPUser object using EnsureUser() method by passing logon (domain\username).

The problem is when a particular user account is disabled in AD, it gives the above exception. 

I need to know if there is some way to know prior OR if any other way to avoid this and also get the SPUser? 

Thanks.

Regards, Nayan