Hi Sean Nagy I am attaching here a new version of your template. I was able to add the checkboxes as shown below.

I think there are two issues causing your errors: function name and field names.
Function names: You are using the function checked, which I replaced with selected*. We are about to add the checked function into the software but it is not available just yet. We are hours away from it... 
- This is what I used: ${Flow_Conditions | selected: "Dry"} Wet
Please note that we will updating the selected and checked functions today. Stay tuned to new announcements in our blog.
Field names: The name in your XLSForm is Flow_Condtions not Flow_Conditions
- This is what I used: ${Flow_Condtions | selected: "Dry"} Wet
In the attached template you will also note that I replaced your curly quotes (”Dry”) to straight quotes ("Dry"). I was able to get things to work with your original curly quotes, but to avoid issues with the parser in the future, I would go with straight quotes.
