Leo, Thank you for your help !!.
The problem seems to be with the Plugin “WP Multistore Builder”, if it is desactived, the GPress Customize Menu is visible, and can work in it.
¿ Do you know, if there is any incompatibility with this pulg in and GPress Premium ?
I have a second question: ¿ To use Gpress Premium, to build an ecommerce activating WooCommerce check box when configure the pluin, ¿ is neccesary to install and activate the original Woocommerce Plug in in WordPress ?
Thanks again for tour help.