Bug 214212 Problem occurs when set the masterpage margin with ems/exs/pixcel units.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/DimensionPropertyType.java
/**
	 * Converts the dimension property value to double value. The dimension
	 * measure will be converted into the session unit.
	 * 
	 * @return double value of the dimension value in session unit. Return
	 *         <code>0.0</code> if <code>value</code> is null.
	 * 
	 */
	public double toDouble( Module module, Object value )
	{
		if ( value == null )
			return 0.0;
		if ( value instanceof String )
		{
			try
			{
				return Double.valueOf( (String) value ).doubleValue( );
			}
			catch ( NumberFormatException e )
			{
				return 0.0;
			}
		}
		DimensionValue dim = (DimensionValue) value;
		if ( DimensionValue.DEFAULT_UNIT.equalsIgnoreCase( dim.getUnits( ) ) )
			return dim.getMeasure( );
		return DimensionUtil.convertTo( dim.getMeasure( ), dim.getUnits( ),
				module.getSession( ).getUnits( ) ).getMeasure( );
	}
}