save error trying set to a non-blob type

I've never tried this API before, but maybe you need to save your data following a sequence of contiguous blocks, which start at zero? Maybe you can't reach block 7 right now?

The file SAVE.SAV in the game folder was corrupt. After I deleted them, everything was ok again.

When saving numbers or strings, it verifies that the thing stored in there before was indeed also a number or string, to prevent accidental variable mixing of things. Deleting the SAVE.SAV works, for this!