E-mail attachments never loading

Just started having this issue a couple days ago. I have not to my knowledge changed any setting on my iMac
When I attach a file of any type (word, pdf, photo, etc) and of any size (larger to tiny) I get a box that pops up saying I can't send the email until the attachment finishes loading. I have never had this to happen. just a couple days ago. The problem is it never will load. I have searched for all types of solutions and I am at a loss. Any ideas / thoughts / suggestions?

Thanks in advance.

What version of OS are you running? What app are you using for mail?

Lisa

Lisa,
Using Sierra. Using the mail format on the computer. I have three distinctive e-mail accounts, yahoo, gmail and a work exchange e-mail on my computer. I get the same message on all 3 e-mail accounts when I try to attach a file.

This is the box that pops up

DownloadedHigh Sierra and everything is fine now.

Check out this post. They may have found a solution:

https://discussions.apple.com/thread/7705498?start=0&tstart=0

Also one solution I found said to reset the nvram: https://support.apple.com/en-us/HT204063

Lisa