Audio Hijack Pro: assiging input device

I have created a scheduler for Audio Hijack Pro. The strange thing is, I get an error doing this:

set input device of theSession to (first audio input whose name is “Built-In Input: Line In”)

Error: "audio input 1 of session id … whose name is … can’t be converted to type reference (translation from Dutch error message).

Has anyone got an idea how to solve it? The example from Audio Hijack help is:
set input device of deviceSession to (first audio input whose name is “Built-in Audio: Internal microphone”)
set output device of deviceSession to (first audio output whose name is “Default System Output”)

the problem might be “theSession” vs. “deviceSession”, but that one isn’t declared and since I’m an applescript novice (just got my definitive guide yesterday" I don’t fully understand the applescript constructions yet.

It is created like this:
set theSession to make new audio device session at end of sessions

Model: Mac Mini (intel(
AppleScript: ?
Browser: Firefox
Operating System: Mac OS X (10.4)

I solved those issues, nevertheless new issues are coming up:

if using the M-Audio USB device as input, the silence monitor doesn’t work correctly but thinks that the input is silent all the time.
Is there a way to solve this?