Where is the pathname fragment: data/dict/test.idx being written to on the PC and on the Kindle?
(I.E: what is the full pathname in each case, working and non-working?)
Also check for differences in the permissions on both.
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Have you inspected the lines in the JSON.lua error report?
Code:
# JSON data cannot be decoded frontend/JSON.lua:525: frontend/JSON.lua:240: can't parse JSON at char 1 of: save to cache data/dict/test.idx
(I.E: perhaps 'save to cache' is not implemented in JSON.lua)
Ah...
Are you using the same JSON.lua on the Kindle as on the PC?