Please try the following before requesting assisting help from ITOPS:
To start they will need to have identified a user who can co-author and one who can't so we have something to compare.
A basic test to identify whether it's a user or computer setting that is preventing the co-authoring from working is to get the working user to log onto the computer of the non-working user and test co-authoring (with a 2nd working user). The 1st working user will need to be logged into Windows as themselves, not just into Breeze to make sure all GPO settings are applied for that user. If the working user can co-author on the non-working users machine then it's a user setting that specifically applies to the non-working user. Continue to step 3. If the working user cannot co-author on the non-working user's computer then it's more likely a Computer setting, jump to step 4.
The next step would be to pull a list of User based GPO's applied to both the working and non-working users when logged onto the non-working user's computer. This can be achieved by running the following command from an elevated (run as admin) command prompt when each user is logged on:
This will output to screen. Find the User Settings section and look at the list of applied group policy objects. It should look like this:
With the working user logged onto their own computer and the non-working user logged onto their own computer, pull a list of Computer based GPO settings that are applied to both the working and non-working user's computers. Please note that for the user to be able to retrieve the Computer GPO settings they will need to be part of the local admins group on their own machine to do this test. It can be removed again after testing. To pull the list of GPOs' applied run the following command from an elevated (run as admin) command prompt
This will output to screen. Find the COMPUTER Settings section and look at the list of applied group policy objects. It should look similar to this:
Compare the list of applied user/computer policies between the working and non-working users. Any user/computer policies applied to the non-working user that the working user does not have applied would be the most likely GPO's to start looking through, specifically ones that deal with Office related settings.
If the policies are large and there aren't any obvious settings that might pertain to Office or co-authoring it might be easier to exclude the policy entirely for that specific user and then test co-authoring again. Once you find the offending policy it can then be scrutinized at a lower level.
To get a more detailed output of the actual settings being applied by each GPO the following command can be run from an elevated command prompt:
gpresult /h results.html
This will create an html file (in the current working directory) with all the users GPO settings that are applied.