AD schema update failed

[Christian Frielingsdorf]

Hello, I have a domain where I want to update the AD schema for Office 365 with the Exchange attributes. During testing this in an test environment I got the error "0x20b Schema update failed: duplicate LDAP display name". The affected attribute is CN=MS-Exch-Extension-Attribute-1,CN=Schema,CN=Configuration,DC=.... Because of this error I looked in the schema context for this attribute (powershell and ADSI editor), to find and maybe disable the attribute. But I cannot find the mentioned attribute. Has anyone an idea where I can find the attribute or any other hint to solve the error. Thanks in advance.

[#2]

I found out, that the AD attribute "extensionAttribute1", which is not used in this environment is the one that the Exchange Schema update process identified as the duplicated attribute. Disabling or renaming the attribute helped solving the issue. But I have to investigate deeper in what this attribute is for.