File Sharing between 2 Users on OS X 10.11.3

Hi,

I have two accounts on my iMac but rely on the Shared Folder to have common files between the users. At times if one account opens a file, excel for example, it opens and can be edited but when trying to save indicates that it is "read only" and has to be saved as a separate file name.

I understand it is a permissions issue and I can clear the problem by using Get Info and Apply to Enclosed items but wanted to know how to avoid this in the future?

I have made sure that both accounts have Read and Write access to the folder.

Liam