I've seen this question posted elsewhere on the form, but it didn't answer the specific problem I'm experiencing.

For reasons I cannot figure, I cannot apply a stroke to a pen path (calligraphy and pencil work fine).

Please see the attached. The Fill & Stroke options show every greyed out:

Any help is appreciated.

I'd finish the path. Stroke values apply when the path is completed.

It's my intention to keep the path open since its a fundamental requirements of the illustration.

Isn't this possible?

Sure, you don't need to close the path, just double click or hit enter to finish the path.

I feared it would be a simple, solution and you've proven it to be the case!

Thanks very much.