I have this same problem however, I ALMOST found a fix.

I found a new version of jkey (0.38) that addresses this issue. The readme is as follows:

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Notes for 0.38 (or a small history, as you wish ;) )
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When I installed Omar's LSInstaller 3.x, the jkey module started to
show me a strage message - 'Invalid - x. Error in definition'.
This message was not shown each time but randomly on a !Recycle.
Never used this module before, so it annoyed me, but I didn't want
to switch to the hotkey.dll module, because it doesn't work with the
multimedia keys :(
Today I spent some time and found that this message is showing because
jugg used VkKeyScan function, that relies on the current input
language. Litestep has the own process's keyboard layout, and sometimes
I switched it (LSXCommand forever! ;) ). But there is no Latin 'X' or
'W' letters in Cyrilic alphabet, so VkKeyScan failed.
I added only two lines of code (now it calls the VkKeyScanEx function
with U.S. English keyboard layout after VkKeyScan failed) and everything
works fine for me :)
Probably it will help somebody else :)

So I installed it, and I STILL get the same error message. I do have a "multimedia" keyboard, its a small version or whatever, but why is this continuing to happen. It only happens if I use one of the custom variables in vk104.txt

So, something is wrong with my keyboard mapping or something else...

:( Please help me too!