The NAV DATA OUT OF DATE message in aircraft FMC’s generally results from:
Navdata actually being out of date and needing update via FMS Data Subscription or
Navdata downloaded but incorrectly installed. Please see FAQ - Navdata AIRAC Updates or
The date/time used in the FS being outside the date range of the AIRAC.
Check your FMC and note the AIRAC number and dates. If not current, see para 2.
If flying within the dates, make sure you are not starting with a FS situation or saved flight with date outside the AIRAC date range.
To be extra sure, set the FS to run in System Time. Also check your PC has the correct date/time set.