Just some info in case you guys don't know yet.
I have two 3ds with 2 gateway cards bought at the same time from the same shop and sent together...
3ds 1 is a classic 3ds (first version) with 4.1U FW... and 3ds 2 is a XL one with 4.3U FW.
One of my gateway cards worked fine, and actually was the first one that I updated, using the classic 3ds at 4.1 fw, worked fine as hell, no problems at all. The other gateway just wont update no matter what...
Tried everything possible, like swaping 3ds', swaping SD cards, swaping microsds, every single time I get the same error 00000019, no matter what I do...
Cruise already tried at 4.5, and I had success with 4.1, so that show's it's not FW problem... Although people hate 4.1 I keep it just to see what problems it will show up and never had any with older versions of Gateway (1.2, 2.0.1b, 2.0.2b...) neither with 2.1 Omega...
Also tried the patch 2.1.1 that they sent me on e-mail, didn't work, same error, on both systems (tried both just to be sure...).
The 'faulty gateway' was working perfectly with older FW (and still is, since I had to roll back one of the systems).
Also, just to make it clear: both Gateways are the original ones.
So... Clearly a Gateway Red Card problem... Anyway not sure if this was of any help but I just thought I could contribute on something...