General Description: As soon as the Data Width value is changed, an Error message pops up which says, "No coefficients specified. ROM must specify at least one coefficient in the coe file."
This happens before you get a chance to load the coefficients.
Solution
This is a known problem.
The error does not prevent you from still specifying the desired coefficient values for the module. Click on the "Load Coefficients" button to load a .coe file defining the desired ROM initialization values to get rid of this error.