NX X NX Open application fails to execute in NX 12

When trying to execute a NX Open application in NX 12 there is an error message saying:
"Error in external library. See system log for details". 
And in the log file this error appears:
"System.MissingMethodException: Method not found: '!!0[] System.Array.Empty()'"

Solution

This is an indication that the user has an old version of the Microsoft .NET Framework installed. The required version for NX 12 is .NET 4.6. Installing that version should solve the issue.

Notes and References

NX 12 Release Notes->NX System Information->Platforms->Operating system requirements->Considerations and caveats

Hardware/Software Configuration

Platform: INTL64
OS: window
OS Version: 764SP1
Product: NX
Application: SYSENG
Version: V12.0
Function: NXOPEN

Ref: 002-8001771