why do i keep getting this

[pjaquiery]

put something like the following in a script step:

if (! FileExists (Application.FindMacro ("DIRVAR").Value + "\\" + Application.FindMacro ("FIRSTVAR").Value))
throw "failure"

The Application.FindMacro bit avoids the \ problem.
Note that this assumes that you are using JScript. Something similar works for VBScript but the throw becomes:

Err.Raise 1, Step.Name, "Forcing build failure..."