Well I see that this happends only when I try to load planing for all projects. When I load one project and its subprojects and subactivities planing loads

This is not an issue but a limitation : when you display planning for all projects, display is blocked if number of projects to display exceeds a given number.
This limitation has been applied to avoid Browser freeze (and possibly crash).
You just have to select a project to limit display to this project and its sub-project.
If you have small projects (with less than 10 lines per projet for instance) you can change this limitation in the Global Parameters screen to allow display of more projects. Just take care about possible effects depending on browser capacity.

The message "selectProjectToPlan" seems not to be a good translation for "Max Projects to display exceeded. You must select a project".
A new translation has been proposed for V5.1 : "Seleccionar Proyecto", more explicit but possibly not complete (sorry I don't speak spanish).
If you can propose a better translation, please do 😉

ok I see, thought I messed up something. Yes a better alert message will help to solve this confusion. I propose:

"Seleccione un proyecto. Maximo de proyectos para mostrar excedido"
"Select a project. Max projects to display exceeded"

Hope is not too long, spanish always is longer than english.
Thank you very much!!

Your translation proposale you appear in V5.1
Thank you