When you sketch the last entity to create a closed-profile sketch, it may clash with inferred relations from the other sketch entities. In this case, the dimension for the last sketch entity causes the sketch to be over defined. In SolidWorks 2012, the clashing dimension is changed to a driven dimension.
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SolidWorks 2012: The dimension on the left vertical line that causes the sketch to be over defined is changed to driven |
SolidWorks 2011: The dimension on the left vertical line causes the sketch to be over defined |