Error previewing: "expected string or bytes-like object"

Hi,

I am getting the following error message when I try to preview my form:

We are about to start data collection - would very much appreciate help on how to resolve this!

@sdalle, would you mind sharing your xlsform so that we could have a closer look at it? Maybe you could also validate your xlsform throught this online validator to see if there are any issues with it.