It looks like the [Promo] column in the datasource would be the problem.
I couldn't find what exactly is problematic with this particular column.
As a workaround you may want to create a calculated field and use it instead:
WHEN 0 THEN 'Inactive'
WHEN 1 THEN 'Active'
Hi Yuri Fal,
Thank you for the response. I tried the workaround you suggested, and created a calculated field 'PromoStatus' with the above formula, but unfortunately, it gave me the same error when I used the new variable instead of 'Promo' in the sales prediction.