I get the graph below on ROOT 6.22-02; maybe you need to update to a more recent version, or there is something wrong with the data file you used (not the same you posted here?).
root [0] .x readexample.C
RooFit v3.60 -- Developed by Wouter Verkerke and David Kirkby
Copyright (C) 2000-2013 NIKHEF, University of California & Stanford University
All rights reserved, please read http://roofit.sourceforge.net/license.txt
[#1] INFO:DataHandling -- RooDataSet::read: reading file u_1e5.txt
[#0] ERROR:DataHandling -- RooDataSet::read(static): read error at line 100001
[#1] INFO:DataHandling -- RooDataSet::read: read 100000 events (ignored 0 out of range events)