There's a known issue when you upgrade NeoLoad from 5.0.2/5.0.1 to 5.0.3. If it's what you did, please download the full 5.0.3 installer from Neotys web site and install it on a different folder.
Then for your current test result, go to <NeoLoad_projects>\results\result_<ID> and remove the summary folder.
Open again your project and your test summary should be re-generated.
That upgrade issue will be fixed with patch 5.0.4 that will be available soon.