what is NullReferenceException and How to avoid it?

Question

If somke error occurs i want the system to redirect to some other page and not show he error message.

<customErrors
   mode="RemoteOnly" 
   defaultRedirect="~/Error.aspx" />

This is not working.

Answer 1

Is aClass a Type instance? If so - just check it for null:

if (aClass != null && alMethSign[z].ToString().Contains(aClass.Namespace))