dotProject Gantt chart generation problem

The error:

JpGraph Error. You are trying to use locale (en) which your php installation does not support. Hint: Try to use ' ' to indicate default locale for this geographic region.

This can be solved by setting up the JPGraph Locale in ‘System Admin’> ‘System Configuration’. One needs to wait a little bit, maybe log out from dotProject for the settings to take effect. The thing killed several hours of my time.