Wifi Sync availability is intermittent
Some users have reported that Wifi Sync is intermittent - for example, your iOS device indicates that syncing will be available when the server is available, even though the server is up and running. If this is the case, then we suggest you first follow the troubleshooting steps on Apple's web site -
http://support.apple.com/kb/TS4062
If these troubleshooting steps do not resolve the issue, then our testing suggests there may be a bug within the Apple Mobile Services application (at the time of writing). If iTunes is started or stopped without restarting the Apple Mobile Services service then wifi synchronisation may not be available. iHomeServer can workaround this bug by restarting the "Apple Mobile Service" whenever it starts or stops iTunes.