Copy/paste problem

[cheeryble]

Macbook Air
OSX 10.11.6

I've never had a problem like this before.

Normally I can use command C and command V to copy and paste.

Today suddenly it doesn't work.
Ill amend that.
It won't paste into e.g. Notes, stickies, Word, Mail etc.
It still pastes into text boxes like the one I'm writing in now.
Here's what I could NOT paste in Notes ten minutes ago:

https://parkinsons.co.in/benefits-of-deep-brain-stimulation-treatment-for-parkinsons-disease/

Here it works.

What gives?

thanks