You specified x as a vector, but controlchart doesn't accept x as a vector. controlchart is going to use means and limits, and it can't do this if x is a vector:
From the help:
controlchart(X) produces an xbar chart of the data in X. If X is a
matrix, its rows should be in time order and should contain replicate
observations taken at the same time. If X is a timeseries object,
the sample at each time should contain replicate observations. The
plot displays the means of each subgroup, or collection of replicate
observations, along with a center line (CL) and lower and upper control
limits (LCL and UCL) to determine if the process is in control. The
control limits are three-sigma limits, with sigma estimated from the
average of the subgroup standard deviations.
