In the README file for the Gadgets extension, around line 51 please change
"Note that the internal name must start with an ASCII letter, ..."
"Note that the internal name must start with an ASCII letter, must not be longer than 25 bytes, ..."
per bug 19410 and bug 19408.
(I just experienced this problem on la.wikipedia and it took me a while to find the cause - would have been easier if this (non-obvious) limitation had been documented in the README file in the first place.)
Thank you in advance!