The problem is solved. I refer to the IDE. B4J in the File menu list the last open projects. If one of these projects has been opened on another network, it still tries to connect it. At the opening of any project or compilation, retry this connection until the timeout is reached. I solved by opening many projects residing on my notebook until the project that does not reside on my network came out of the list of the last open projects. Now everything is fine.
I add, B4J when it starts, check that the projects in the list under the file menu are existing. I tried to rename a project and B4J took it off the list. But if the project has a network address, to verify its existence it accesses the network and tries until the timeout is reached. In that case, do not delete it, but try again at every opening or every compilation. This makes B4J look very slow.