Have you ever encounter the issue that the folder is not able to share by group?

I have created two groups, one of them is designed to read only. 7 members are in the group. When I follow the instruction in the help documents in the link.

https://www.zoho.com/docs/help/secure-sharing.html#add-files-to-shared-folders

No group name is allowed to me to choose. Besides, error message "Sharing failed due to unexpected server error. Please try again." shows. 

Any one has any idea?