Invalid Transaction: final gnc_numeric value, using 0 instead

[prl]

When I open my Gnucash accounts file I get a popup with:

    Invalid Transactions

    error -3 in SX [-- scheduled transaction name --] final gnc_numeric
    value, using 0 instead


If I then run Actions>Scheduled transactions>Since Last Run... it causes 
a crash.

I've re-entered the numerical value into the transaction, and I still 
get the same problem.

The transaction created has one of the two account values correct, the 
other blank, and a third split for Imbalance-AUD for the other side of 
the transaction.

I have "Create in advance" and "Remind in advance" both set to 5 days, 
but I have that set like that on most of my scheduled transactions.

Although a transaction is created each time I open Gnucash, the Last 
Occur and Next Occur dates are not changed.

The transaction amount is AUD 1921.70 (value copy/pasted from GnuCash 
Edit Scheduled Transaction window, from the entry that is blank in the 
generated transaction). I only use AUD in transactions. I use '.' for 
the decimal separator (and it works in all my other transactions). Is 
the error in some other value in the scheduled transaction?

The error first occurred today. The scheduled transaction is yearly, I 
think this is its second or third firing.

Gnucash is 2.6.15 (built from rev 1ef17e6+ on 2016-12-17), OS X Intel build.
On OS X El Capitain 10.11.6

Anyone have any ideas?

Peter