Menu OnExecute Event does it support Display message and table data validation

I have a project with Menu. Before any form is opened, I want to validate if the look up table is populated. For eg. I have a User access table and User Master Table . Before data is entered in User Access Table data has to be entered into User Master since I am using User Master as look up to the field in user access.This will be necessary only for the first time usage when both tables are blank… I want to enforce this check at Menu onExecute (I could not get it at form level but would not work) . Can anyone please give some pointers. Honestly I am total novice in this.
I tried to display message at Menu OnExecute which threw an error (using sc_ajax_display, error message) Plain java script code does not show up at all. Thanks to all in advance.