We are running MS Exchange Server 2003 and have 3 clients using Outlook 2007.
Sharing between all 3 were successful (for each pairing) except for one
unable to share with another:

Client 1 can share with Client 2
Client 1 can share with Cliient 3
Client 2 can share with Client 1
Client 2 can share with Client 3
Client 3 care share with Client 1
Client 3 can NOT share with Client 2

The point is only one of these fails with the Mircosoft Office Outlook
message:

"Calendar sharing is not available with the following entries because of
permission settings on your network....Do you want to send them a copy of
this calendar in an e-mail message instead?"

The server administrator swears all permissions between the 3 are identical
including groups they belong to. I've checked permissions within Outlook and
confirmed they were set up correctly. I had someone else double check in
case I just missed something. All to no avail.

Can anyone shed light on what the possibilities are for why this error is
occurring, where to look???

Thanks.