Also, big thing here:
Open up the confidence test on a workstation (Start -> Programs -> Micros Applications -> Confidence Test). You'll then want to select mag stripe and swipe the card.
When it asks for a password, it is first number * second number plus three from last plus last. So if the number if gives you is: 7235459
you do: 7 * 2 + 5 + 9
and then type that number in.
When you swipe the card, it will tell you which track has data. Then go to the next tab and swipe again; it will show you that data.
For example, when I swipe the gift cards we buy from Micros, I get:
Track 1: DATA NOT PRESENT
Track 2: VALID READ
Track 3: DATA NOT PRESENT
And then the actual data looks something like:
;32546987452?
So what this means is that we want to set our gift card to read track two, start at the second character (so that we ignore the

and read only 10 characters (so that we don't read the ?).
To do this, open POS Configurator, go to the GSS tab, and click Card Setup.
Set the Track # to 2, and start position to 2 and 10.
If your gift cards are reading different tracks or differently formatted data, you will of course have to set it to use the format they have.
This is where the invalid serial is coming from (though what I listed in the last post are changes you do have to make for it to work).