I tried similar thing but could not reproduce the problem.
Will you try following to get more information?
root [0] .L ntuple.so
root [1] ntuple *n=new ntuple()
root [2] .L test.cxx
root [3] .debug <<< Add this command
root [4] .T <<< This one too
root [5] n->Draw("x")
Error: No symbol Draw("x") in current scope FILE:/tmp/01521caa LINE:1 (class
ntuple*)0x85073d0
*** Interpreter error recovered ***
root [6] n->Loop(test)
.debug command turn on bytecode debugging mode which will give you a little
more information. Please inform me what it says.
Thank you
Masaharu Goto