int nameNum = book.getNumberOfNames();
for (int i = 0; i < nameNum; i++) {
    HSSFName namedRef = book.getNameAt(i);
    System.out.println("Cell ref = " + namedRef.getReference());
    CellReference cellRef = new CellReference(namedRef.getReference());
}

results in: 

Cell ref = Summary!$D$31
java.lang.NumberFormatException: D$31 	
  at java.lang.Integer.parseInt(Integer.java:426) 	
  at java.lang.Integer.parseInt(Integer.java:476) 	
  at
org.apache.poi.hssf.util.CellReference.<init>(CellReference.java:82)

because it doesn't seem to be parsing the string right (it doesn't pass
over the sheet name before trying to parse row/col information out.

Patch is attached.