>Sadly the only error message I see is "invalid map item"

Common mistakes I have made;

• Forgetting to have an 'endmap' statement
• Mixing scraps and maps within the same map definition
• Missing a dash at the start of an option such as ‘-title’
• Forgetting one of more “ surrounding a string (such as in -title “map title string”)

But looking at your original post, I think maybe you have a join inside a map definition.

Joins should be inside the survey, not inside the map.

Brue