Root Rooted but su says "Permission denied"

[monnier]

I have this A2107 tablet which I rooted with the 4.03root.zip method (tho running the root.bat script by hand from my GNU/Linux machine) and that worked fine.

Then I passed this tablet to my daughter for a couple years, and now I got it back.

/system/bin/su is still present, still the same date and size, still mode "rwsr-sr-x", so all looks fine, but when I try to run it from a shell, it just tells me "Permission denied".

Any idea what might be going on?