I am making a map in print composer. I am trying to add the scale bar and it's appearing as a box with a zero digit inside it. What should I do to make it display properly?
In the object properties (the scale bar) you must set two values, "segment size" and "map units per bar unit" (this second option is do for example a scale in KM rather then meters). In the next QGIS version there will be the option to force the scale be in meters or feet even when the project CRS is lat/lon.