Maybe try this:
if your 5.0.3 is not the same as Service pack 3:
download Service Pack 3 (besx_upgrader_5.0.3.exe, 879mb), install this, and then again install the maintenance release 8

or:
Make a backup of the database, uninstall the Blackberry server (keeping database and besadmin information/passwords, the installer normally wont delete the database).
Before uninstalling make a note about the database and the connection method.
install 5.0.3 again, download and install Service pack3 (if your 5.0.3 is not the same as Service pack 3 879mb), point the installer to the database, then install any needed updates.