Bar borders are dotted.

 In rare circumstances Prism bar graphs can end up with dotted borders. Here is a work around: 

1. Double click on your graph to bring up the Format Graph dialog.
2. Click ALL so changes affect all data sets
3. Change the graph type to scatter dot plot Look below in the lines section and see that the lines are set to dotted. That is the cause of the problem.
4. Change to solid lines.
5. Change the graph type back to a bar graph.