My Tektronix DPO 4104 sends an unexpected preamble:
The point_enc is expected to be "BINARY" but the scope sends "BIN".
Changing line 1296 in tektronixBaseScope.py from:
if point_enc != 'BINARY':
to:
if point_enc != 'BINARY' and point_enc != 'BIN':

fixes the problem for me. I can then communicate with the scope and fetch waveforms.
The scope has the latest firmware (2.68) and I was using the git version of python-ivi (commit cfa45ce on 18 Feb 2017 ).