I'm not certain that I can log into the same Wolfram cloud that you are using, but perhaps you can try these steps in the cloud and see if you get the same results that I do.

If I go here

[http://develop.open.wolframcloud.com/app/][1]

and click "Create a New Notebook" in the lower right corner

and wait for that to load and stabilize

and then paste

data = RandomVariate[NormalDistribution[0, 1], 1000];
EstimatedDistribution[data, NormalDistribution[mean, stdev],
ParameterEstimator -> {"MaximumLikelihood"}]

all in one long line and wait for that to appear and to stabilize and then click Evaluation on the menu bar and click Evaluate Cells in the drop down menu

then in a fraction of a second I get

NormalDistribution[0.023417332720967812, 0.9942659649019443]

That seems to be similar to what you are trying to do and it seems to eliminate some uncertainty about whether there are errors in the code you showed.

There are time and memory limitations on the use of that cloud page, but perhaps this can help you make a little progress.