Need help with Data/Chart Widget

I am working on a dashboard with various data points and had zero issues until I started the most recent widget. I am pulling from a simple report that has a list of staff members and their assigned work spaces. I keep getting an error that says the data cannot be charted… What is the limitation here? I made 4 other reports that list room number and population and this charts fine… Does the data have to be numerical in some way? At a total loss as to why it's complaining.