LDAP plaintext auth - Missing externalID

I have a brand new Server 4.1 setup on 10.10.3, it is setup to authenticated against an external LDAP server which is working flawlessly. I followed the instructions, here, to setup 'plaintext' authentication. Trying to authenticate to the Wiki I get the following error:

<Error>: [CSServiceDispatcher.m:261 125e9000 +393ms] Caught exception "Missing externalID" [CSAuthServiceError] executing [http]Request{AuthService.validateUsername:andPassword:remember:(<<scrubbed>>)}:
    (
        0   CoreFoundation                      0x00007fff8de5a03c __exceptionPreprocess + 172
        1   libobjc.A.dylib                     0x00007fff90a3976e objc_exception_throw + 43
        2   CSService                           0x000000010f8c5775 -[CSAuthService whoAmI] + 0
        3   CSService                           0x000000010f8bf0a5 -[CSAuthService sessionForUsername:andPassword:remember:] + 568
        4   CSService                           0x000000010f8bedb3 -[CSAuthService validateUsername:andPassword:remember:] + 96
        5   CoreFoundation                      0x00007fff8dd317bc __invoking___ + 140
        6   CoreFoundation                      0x00007fff8dd31612 -[NSInvocation invoke] + 290
        7   CSService                           0x000000010f83bc4d -[CSServiceDispatcher executeRequest:asPartOfBatch:usingServiceImpl:] + 4774
        8   CSService                           0x000000010f83c72e __43-[CSServiceDispatcher executeBatchRequest:]_block_invoke_3 + 83
        9   CSService                           0x000000010f841832 -[NSArray(CollabBlockMethods) map:] + 249
        10  CSService                           0x000000010f83c687 __43-[CSServiceDispatcher executeBatchRequest:]_block_invoke_2 + 160
        11  CSService                           0x000000010f841f10 +[CSExecutionTimer recordTime:ofBlock:] + 74
        12  CSService                           0x000000010f841d4b +[CSExecutionTimer timerNamed:aroundBlock:] + 76
        13  CSService                           0x000000010f83c3d4 __43-[CSServiceDispatcher executeBatchRequest:]_block_invoke + 323
        14  PostgreSQLClient                    0x000000010f793e03 -[PGCConnection transactionInBlock:onError:] + 149
        15  CSService                           0x000000010f83c20a -[CSServiceDispatcher executeBatchRequest:] + 277
        16  CSService                           0x000000010f8b293b +[CSServiceDispatchHTTPRouter routeServiceRequest:response:] + 1024
        17  CSService                           0x000000010f8427ae __21-[CSServiceBase init]_block_invoke_6 + 48
        18  CSService                           0x000000010f8af984 __53-[CSRoutingHTTPConnection httpResponseForMethod:URI:]_block_invoke + 92
        19  CSService                           0x000000010f8b2f7a -[CSHTTPBackgroundResponse bounce:] + 284
        20  Foundation                          0x00007fff8ce31dc2 __NSThread__main__ + 1345
        21  libsystem_pthread.dylib             0x00007fff97253268 _pthread_body + 131
        22  libsystem_pthread.dylib             0x00007fff972531e5 _pthread_body + 0
        23  libsystem_pthread.dylib             0x00007fff9725141d thread_start + 13
    )

So far I haven't been able to find any information regarding this. Anyone have any ideas?