Can't add collaborators - Get message: "Something went wrong. Please try to add collaborators again."

When I try to add collaborators to a folder for which I am a co-editor, I get the pop-up. 'Something went wrong. Please try to add collaborators again."  This is on a folder to which I have already added all 98 of its existing (100) collaborators, so being rejected all of the sudden is strange.  In attempting to troubleshoot this myself, I've tried all manner of data entry for the email addresses, including copy-paste, typing it in myself, adding multiples or just a single address at a time.  To verify it was not an issue with the email address, I removed and tried to re-add an email address that already had access (a secondary one of my own) and I received the same pop-up rejection.  I also tried the old standby solutions for any tech issue: logging in and out, searching Box support, Googling the issue, and waiting it out a day, to no avail.  This issue has already persisted for a day, so I don't expect it's a temporary system glitch that will resolve itself.  Anyone have ideas?