The machine where OptiSurface Designer V2.5 was installed previously was formatted. It was reinstalled without issues but when opening previously saved files or importing new survey files, it does not allow calculation then crashes and the operations under Tools were greyed out as shown in the image:
Make sure Windows is properly updated using Windows Update. Windows update have some issues sometimes taking too long to search for updates. Some symptoms include high processor and memory usage for windows update (svchost.exe).
If this is the case, let Windows Update run overnight or more until it searches updates and install them. Make sure Windows is up-to-date and it says 'There are no more updates available for your computer.'