Why do I receive "Error using RectangularQAMModulator"

% Set the OFDM and QAM parameters
N = 64; % Number of subcarriers
M = 16; % Size of QAM constellation
CP = 16; % Cyclic prefix length

% Set the number of nodes in the network
numNodes = 4;

% Set the frame length and number of slots
frameLength = 1000;
numSlots = numNodes;

% Create an OFDM modulator object
ofdmMod = comm.OFDMModulator('FFTLength', N, 'NumGuardBandCarriers', [0;0], 'CyclicPrefixLength', CP);

% Create an OFDM demodulator object
ofdmDemod = comm.OFDMDemodulator('FFTLength', N, 'NumGuardBandCarriers', [0;0], 'CyclicPrefixLength', CP);

% Create a QAM modulator object
qamMod = comm.RectangularQAMModulator('ModulationOrder', M, 'NormalizationMethod', 'Average power');

Warning: COMM.RECTANGULARQAMMODULATOR will be removed in a future release. Use QAMMOD instead. See this release note for more information.

% Create a QAM demodulator object
qamDemod = comm.RectangularQAMDemodulator('ModulationOrder', M, 'NormalizationMethod', 'Average power');

Warning: COMM.RECTANGULARQAMDEMODULATOR will be removed in a future release. Use QAMDEMOD instead. See this release note for more information.

% Generate a random data sequence for each node
data = randi([0 M-1], frameLength, numNodes);

% Modulate the data using QAM
modData = qamMod(data);

Error using RectangularQAMModulator
The input must be a column vector.

% Modulate the QAM symbols using OFDM
txSignal = ofdmMod(modData);

% Perform DCT on the OFDM symbols
txSignal = dct(txSignal);

% Create a TDMA schedule
schedule = repmat((1:numNodes)', 1, frameLength/numSlots);
schedule = schedule(:);

% Transmit the data using TDMA
txSignal = txSignal(:,schedule);

% Add channel noise to the transmitted signal
rxSignal = awgn(txSignal, 10);

% Perform IDCT on the received signal
rxSignal = idct(rxSignal);

% Demodulate the received signal using OFDM
rxModData = ofdmDemod(rxSignal);