Multiupload failed to load. An issue occured....

I've had to upload pictures one at a time for quite a while now with both Explorer & Firefox.

How can I bulk add pictures to my gallery? This is what I get when I open the bulk load pictures screen
I tried to select files & start the upload, but it still gives me the same message.

What device are you trying to upload from?

Have you tried smaller file sizes?

What device are you trying to upload from?

Have you tried smaller file sizes?

From our PC. File size is 100 to 250 KB per picture. It used to work.