In 17.5 I can't select the points while using the Edit Capture Weights tool, any idea why? Thanks

Had the same problem a couple of days ago, it's probably a bug.
It has been reported as Bug ID=#95836

The Edit Weights tool works at the object level - not SOPs
when I try to reproduce this and select “Edit Capture Weights” from the Rigging shelf while in SOPs - I'm popped up to the Object level and can select points to edit.
is that what you're seeing?

The problem is, that this doesn't work, when secure selection is on (which it is by default since H17 I think). The tool won't accept any input then, after bumping you up to OBJ level.