Lion Server iCal Issue -- CoreDAVHTTPStatusErrorDomain Code=405

I have Lion Server set up with iCal Server enabled/running. I've set up a iCal client and it frequently gets this error when syncing:

The server responded with an error.

http://zmac.home/principals/__uids__/54FCAB02-50E8-45DB-8437-CD011076B055/ is not a location that supports this request.

When I look at the console on the server, this is the error that shows up there:

2011-10-16 7:30:33.191 AM iCal: Account refresh failed with error: Error Domain=CoreDAVHTTPStatusErrorDomain Code=405 "The operation couldn’t be completed. (CoreDAVHTTPStatusErrorDomain error 405.)" UserInfo=0x7fe3419c36e0 {CalDAVErrFromRefresh=YES, CoreDAVHTTPHeaders=<CFBasicHash 0x7fe3419be970 [0x7fff71e10f40]>{type = immutable dict, count = 7,

entries =>

0 : Case Insensitive Key: Server = <CFString 0x7fe34193a2c0 [0x7fff71e10f40]>{contents = "Apache/2.2.20 (Unix) mod_ssl/2.2.20 OpenSSL/0.9.8r DAV/2"}

1 : Case Insensitive Key: Content-Type = <CFString 0x7fe341939f00 [0x7fff71e10f40]>{contents = "text/html; charset=iso-8859-1"}

2 : Case Insensitive Key: Allow = <CFString 0x7fe33fc9fca0 [0x7fff71e10f40]>{contents = "GET,HEAD,POST,OPTIONS"}

6 : Case Insensitive Key: Date = <CFString 0x7fe3419c6870 [0x7fff71e10f40]>{contents = "Sun, 16 Oct 2011 14:30:33 GMT"}

10 : Case Insensitive Key: Keep-Alive = <CFString 0x7fe3419c4cf0 [0x7fff71e10f40]>{contents = "timeout=15, max=100"}

11 : Case Insensitive Key: Content-Length = <CFString 0x7fe3419c2020 [0x7fff71e10f40]>{contents = "395"}

12 : Case Insensitive Key: Connection = <CFString 0x7fe3419b7b10 [0x7fff71e10f40]>{contents = "Keep-Alive"}

}

, AccountName=Mac OS X server}

Does anyone know what this might indicate and how to resolve it? zmac.home does resolve properly to the IP address of the Lion Server.

Thanks in advance.