On the ServiceDesk Server please access the registry and update the below key to use the following value:
HKEY_LOCAL_MACHINE\Software\Wow6432Node\NetSupport Ltd\DNA Helpdesk\ADSSync\
Value name: LogLevel
Please could you then access the ServiceDesk, untick the ADSync option and click Save. Then enable this again and click Save (by turning this off and then on again it forces the ServiceDesk to perform the Sync).
Once performed there should be a log file created in the following :
C:\Program Files (x86)\NetSupport\NetSupport Service Desk\LogFiles\