Can't attach files to emails

This started happening a few weeks ago, under 7.2.2, I’d click ‘attach’ and I’d browse for a file, click upload, then the browse dialog clears but remains on screen and nothing gets attached. I don’t see any errors in the webserver or suitecrm logs.

I thought I might as well update and see if the problem clears up so I upgraded to 7.4.1 and that did not fix it. So I used the quick repair and rebuild tool and that did not fix it.

Can anyone suggest what might be wrong? email attachments were working before.