Help With VLOOKUP

This is part of a formula I am working on:

if(or(iserror(vlookup(a1,Exceptions!$a:$c,3,0)),vlookup(a1,Exceptions!$a
:$c,3,0)=""),"Do step A","Do step B")

The formula does not evaluate correctly with the second VLOOKUP when
the value in A1 is not present in the Exceptions tab.

This is because the OR function evaluates to: OR(TRUE,#N/A), and
therefore the final output is also "#N/A".

How can I corrct this?
--
tb