You can use a session condition on your dashboard.
1) Into your dashboard you must have your report and a "message" in two separate sessions, cause you must define different conditions for them.
2) On your prompt set a presentation variable for "Rank to" and "Rank from". These variables must be passed to an auxiliary analysis. (create a filter on this analysis that results in one record to true values (based on conditions mentioned above) and no record for other ones
3) Use a count of rows from your auxiliary analysis to define your session conditions
4) <RESULTS> When some user type a wrong value the "message" will appear. When some user type a correct value the report will appear.
Please Mark if help you.
thank you felipe i will try it first,,once again thanks for sharing your idea.