There are limitations to what can be placed in menu item names, form captions, query captions etc. The expressions used there can only use the context of the current object (for forms), context used in queries (for queries) plus LoggedInSystemUser and SystemSettings
For menu item names the only available context is LoggedInSystemUser and SystemSettings.
Any aggregate operations are not allowed. So if you want to use them you need to create an attribute in your user object or SystemSettings (depending on what the aggregate expression involbes) and add a rule to the object to calculate it and then use it in the menu