Changing sorting leads to unclear error

[josephwright]

As reported in http://tex.stackexchange.com/questions/347416/empty-bibliography-after-changing-style-to-chem-acs, swapping the sort order after an initial Biber run gives the rather unhelpful error

(./<name>.bbl
! Undefined control sequence.
<argument> \blx@tempa 
                      
l.<line>\endrefsection

At the very least, a more helpful message should result.

[plk]

Hmm, not obvious how to handle this - do you have any ideas?

[josephwright]

@plk Yup, that's my job on the biblatex team: deal with tricky TeX issues :)