iMacros help

I was working on a macro to guess this particular code:
CowBoyBeebopXvj5ks21o73kdp4if9md5jp47???? (number, letter, letter, number)

The macro is done in imacro.
For my macro I have a file in datasources folder called input.txt. It has a copy of every possible combination, like this:
[iOpus]
name0=0
name1=0aa0
name2=0ab0
name3=0ac0

My code is:
SET !DATASOURCE input.txt
SET !VAR1 CowBoyBeebopXvj5ks21o73kdp4if9md5jp47{{name!LOOP}}
TAG POS=1 TYPE=INPUT:TEXT FORM=NAME:regf ATTR=ID:register_username CONTENT={{!VAR1}}
TAG POS=1 TYPE=INPUT:SUBMIT FORM=ID:regf ATTR=NAME:Submit&&VALUE:I<SP>agree<SP>-<SP>continue<SP>sign<SP>
;up
wait seconds=1

However the string it actually inputs is: CowBoyBeebopXvj5ks21o73kdp4if9md5jp47__undefined__

Question is:  How do I get it to put out the string as you may have guessed I want it being output like?

I'm sorry if I broke any rules of this board.

I daren't say that I couldn't find them.

Essentially what I am doing is trying to solve the pattern [[:digit:]][[:alpha:]][[:alpha:]][[:digit:]].

I have generated a text file with all combinations and I have named every combination, from "name0" to "name67600".

When I try to get these into the add on "iMacros" it doesn't work. 

I would like someone to explain what is wrong with my code and what is needed to fix it.