Solution
This error has been seen when some general .NET framework assemblies are included as part of a LabVIEW project under the My Computer node, so LabVIEW may think they are part of the source code and fails to provide an absolute path as these are usually referenced by name. Some of the cases included mscorlib.dll and system.dll, core components of Microsoft .NET Framework.
If you have manually included any system .NET DLLs under My Computer, please right-click them >> Remove from Project, this will move them back into Dependencies and should fix this error.