This seems to be related to: https://emacs.stackexchange.com/questions/15185/cant-assign-to-hline-relative-reference

There seem to be restrictions regarding hline-relative-references within table-formulas.

If change 'I' and 'II' for 1 and 2 on the very left of the formula, it works (keeping the other hline-relative parts) . If I stay with the former I get the same error as you (emacs 26.1, orgmode 9.1.9, Debian stable).

I hope this can help, 
Daniel


Am 21. Oktober 2020 03:14:10 MESZ schrieb Dante Catalfamo <dante@lambda.cx>:
>Hello,
>
>I'm trying to create a table where the third column between two hlines
>is set by a formula referencing the second column.
>
>Here is an example:
>
>| a     |     b |      c |
>|-------+-------+--------|
>| row 1 | 12.00 | 144.00 |
>| row 2 |       |  23.00 |
>|-------+-------+--------|
>| sum   | 12.00 | 167.00 |
>#+TBLFM: @I$3..II$3=if($2 != 0, 12*$2,
>$3);%.2f::@4$2=vsum(@I..II);%.2f::@4$3=vsum(@I..II);%.2f
>
>When I try to calculate this table however, I get the error "Can’t
>assign to hline relative reference".
>
>Why is this now allowed? This seems like a fairly mundane use of a
>table to me. It is explicitly disabled in the source, but without
>explanation, and searching the mailing list doesn't turn up many
>answers.
>
>Is there a recommended way to handle a situation like this?
>
>Could this feature be fixed?
>
>Thank you,
>Dante

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