Steve,
Not a great situation to be in, I can understand that. I hope you didn't order a production quantity...
There are a good few solutions, but the two most obvious to me are:
1. Move production back to Chempix. If they can produce the fret, use 'em.
2. Copy the artwork and amend it to allow for greater etching tolerances or (more to the point) greater variability in the etching tolerance. I.e. you want 'graceful degradation' if the fret over etches in that it remains useable even if this happens. I also agree with DJP on the subject of tabs, you probably need a few more to prevent parts being snagged off, but it may only be worth making that change if you're playing with the artwork for other reasons.
As an aside, it is very rare in production terms to be able to shift suppliers for bespoke items. Different manufacturers will have different ways of solving the problems and producing items. It doesn't matter whether we're talking about photo-etched brass sheets, lost wax castings or (my experience) printed circuit boards, motion picture film, audio cables, integrated circuits, etc. etc. If a client starts talking about moving production to alternative sources that's the point at which things start to get 'interesting'*!
I hope G&H have provided you with some more positive feedback than just 'it's wrong' so you can apply their thoughts - it has the potential to help so your etch tool becomes more tolerant of production variance/deviation**.
Steph
* For which read 'the point at which Dale has to demonstrate he's worth his fee'!.
** You're actually in to 'deviation' territory here; the processes used to produce frets at Chempix will be different to those used at G&H.