To resolve above issue,
Uninstall and ReInstall the Microsoft.NET in your system
Ahmad, Share as much information with us that you think might be relevant. For starters the information of button ‘Details’.
One suggestion: “Object reference not set to an instance of an object” might point to a missing database-object. Try App->Settings->Doubleclick the configuration->change the dabasename. Though since this error is reported by .Net, this might not solve your problem. Worth a try though.
Second suggestion: upgrade to a higher version, 9.17 or 9.18.