Error occured filling form - "incorrect usage of calculations in the form design"

Hi Dears,
We have a question in the designed form that is set as follows:
We have tested both the following formats for the question type:
name= text and appearance=numbers
name= integer
It works correctly in the web version. But in app version of the program, we encounter the following error:

could you pls help me?

It might be preferable for your support to avoid posting to ODK forum and KoboToolbox forum at the same time, please. See

I have encountered the same error when I had some bad calculations into selects before so my guess here is that you are calculating a value into a select, but one of the values is invalid.

Looking at the screenshot in your other post, your possible outcomes from the calculation are [1, 2, 3, 4, blank]. Do your choices for a2 match this?

Hi @ahblake,
Problem seems solved (before) already, see