Unable to create Skype meetings on delegation even though I have the proper rights on Outlook

Hello,

We are facing an issue with one of our infrastructures. Our servers are running Skype 2015 with clients using Skype for Business 2016 on their computers (Don't ask me why, we acquired the clients this way and they don't want to change :D).

For 3 users out of more than 3000, we are experiencing problems with Skype delegation through Outlook when trying to schedule Skype meetings. Every time they attempt to create a Skype meeting for the person they have delegated for, they receive an error stating that they do not have the rights to do so... even though they do.

We have:

• Verified the SIP addresses and everything is okay.
• Deleted and re-created the sharing, but the issue persists.
• MAPI connection on the Skype clients is functioning correctly.
• Tested with a new Outlook profile, which worked fine.

If anyone has any ideas, I would greatly appreciate it!!
Thanks a lot