if I write
Ext.state.Manager.setProvider(new Ext.state.CookieProvider()); //SAVE columns property after refresh
In spite of the fact that I am new in Sencha and this forum, I made some investigation and its result is presented here.
First, I had a deal with the error "Cannot call method 'getWidth' of undefined" during the try to use hide() or setVisible() functions. Both of them uses the following code:
As the result, the error occured since el object is undefined.
When I found it, the next step was to check this object at each stage of the grid initialization flow. The property el was initialized at rendering stage after calling parent method. Once it is initialized, the methods setVisible() and hide() are working propertly.