As I've written before, I couldn't preview some kind of files and downloading them neither (not just some extensions but all). I don't really know if it's a real bug or not but i've saw other people whith the same problem.
To solve it I've just changed the return value at "./lib/galaxy/web/controllers/dataset.py", at the "display" function (or method).
In stead of returning the value returned by "open()" function, I do return the value returned by "read()" function.
Originaly: ... return open(...) ...
New: ... return open(...).read() ...
Well, i don't know if its beacause of my system but i wish this can help
Saludos Alfonso
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