i've installed osx server on an iMac in my lan, and I activate TimeMachine service on an usb Lacie 500GB.
On my macbook pro (osx lion) I've opened time machine, in disck menu window I've selected time machiene network disk on server and backup start without any problem.
On a second macbook pro (osx mountain lion) I've do same operations but when beckup start I have as error message "Back Up Disc Not Available". I have update disk name, disabled and re-enabled time machine, mount disk with cmd+k and changed disk in time machine but I still have the same problem.
On a third iMac (osx lion) i have the same error, seems that backup works only on my personal macbook. Can anyone help me? any ideas?