BUILD problem

Using Visual Studio 2019 CE and Visual COBOL PE.

I have a series of programs which compile without errors. After a short break I fired up the project in VC and  was confronted with this error message:

''The "MicroFocus.Cobol.BuildTasks.AssignSourceTargetPaths" task could not be loaded from the assembly C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Micro Focus\Visual COBOL\v1.0\MicroFocus.COBOL.BuildTasks.dll. Method 'get_SourceFileExtension' in type 'MicroFocus.COBOL.BuildTasks.CreateCobolManifestResourceName' from assembly 'MicroFocus.COBOL.BuildTasks, Version=, Culture=neutral, PublicKeyToken=0412c5e0b2aaa8f0' does not have an implementation. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.''

The program in question compiles without errors bu t I cannot run it because of the foregoing error message. I tried a Visual COBOL Repair but this has made no difference.

Seems very strange that this error has only just revealed itself.