Found No Video Players That Supports The Given Video Format

Hi - In the last few days I've been unable to replace some of the videos in my interactive video activities. I copy from my Vimeo Pro account the video file URL and paste it in 'step 1' on the upload/embed video section as I have done for months and months with no issues. Now when I do this I get an error "Found No Video Players That Supports The Given Video Format" - I'm trying to link to content on my Vimeo account, the account is Pro so it has and should continue to support all external video sources. Any advice please? I've tried creating a new project thinking it might just be the project I'm trying to amend that could be corrupt but it gives the same error on all interactive video projects. It's worth advising that videos from YouTube are fine. Please help. Thanks.