Can you confirm that MATLAB is using the version from DSP System Toolbox and not the one from MATLAB or that you've created or downloaded? Run this command with the X on which you're trying to operate in the workspace:
which -all normalize(X, 'range')
I don't think the version of normalize in DSP System Toolbox even calls sum, and line 10 of the one included in MATLAB is a help text comment. I think you have a different normalize.m that's shadowing the one in MATLAB. Rename that normalize.m, remove it, or move it lower on the MATLAB path than the one in MATLAB.