msb@msb:~/Music/Examples/ROOT_Plot$ root -l ./MergePlot.C
root [0] 
Processing ./MergePlot.C...

 *** Break *** segmentation violation



===========================================================
There was a crash.
This is the entire stack trace of all threads:
===========================================================
#0  0x00007fde288ea45a in __GI___wait4 (pid=386470, stat_loc=stat_loc
entry=0x7ffdfad4f898, options=options
entry=0, usage=usage
entry=0x0) at ../sysdeps/unix/sysv/linux/wait4.c:30
#1  0x00007fde288ea41b in __GI___waitpid (pid=<optimized out>, stat_loc=stat_loc
entry=0x7ffdfad4f898, options=options
entry=0) at ./posix/waitpid.c:38
#2  0x00007fde28850bcb in do_system (line=<optimized out>) at ../sysdeps/posix/system.c:171
#3  0x00007fde29312344 in TUnixSystem::StackTrace() () from /home/msb/Music/root-6.26.06/obj/lib/libCore.so
#4  0x00007fde2930f655 in TUnixSystem::DispatchSignals(ESignals) () from /home/msb/Music/root-6.26.06/obj/lib/libCore.so
#5  <signal handler called>
#6  0x00007fde12ae5988 in TMultiGraph::Add(TGraph*, char const*) () from /home/msb/Music/root-6.26.06/obj/lib/libHist.so
#7  0x00007fde28e2d3a4 in ?? ()
#8  0x000056279c6763e0 in ?? ()
#9  0x000056279c5b04f0 in ?? ()
#10 0x00007fde2489ee60 in ?? () from /home/msb/Music/root-6.26.06/obj/lib/libCling.so
#11 0x000000659c737590 in ?? ()
#12 0x000056279ea9ced0 in ?? ()
#13 0x000056279db41d50 in ?? ()
#14 0x0000000000000000 in ?? ()
===========================================================


The lines below might hint at the cause of the crash.
You may get help by asking at the ROOT forum https://root.cern/forum
Only if you are really convinced it is a bug in ROOT then please submit a
report at https://root.cern/bugs Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#6  0x00007fde12ae5988 in TMultiGraph::Add(TGraph*, char const*) () from /home/msb/Music/root-6.26.06/obj/lib/libHist.so
#7  0x00007fde28e2d3a4 in ?? ()
#8  0x000056279c6763e0 in ?? ()
#9  0x000056279c5b04f0 in ?? ()
#10 0x00007fde2489ee60 in ?? () from /home/msb/Music/root-6.26.06/obj/lib/libCling.so
#11 0x000000659c737590 in ?? ()
#12 0x000056279ea9ced0 in ?? ()
#13 0x000056279db41d50 in ?? ()
#14 0x0000000000000000 in ?? ()
===========================================================