Users were trying to: add units to a numerical value (like height).
What actually happened: users often put the units directly into the value field which resulted in a grayed out save button and no feedback on what was wrong.

Proposed solution: Ideally we would like to be able to parse their input and suggest units based on what they've entered. At minimum it would be good to provide some feedback about why they can't save like "you've entered a letter in a number field"