In a Multiple choice question with the comment field.
In my project it should have all the checkmarks on (pre defined) and people are allowed to uncheck them.
If the do so, they should write in the comment box the reason why they uncheck.... but ....alas... the unchecking the box disables the text box... is there a work around?

Yes. Use a mc field without comment box. Add a multiple short text field, that has an exclusion array filter on the mc field. See simple example
Success!
Frans Marcelissen, DigiPsy