Office 365 AAD Sync

We have migrated a SBS 2008 Exchange to Office 365 and have installed AAD Sync on a member server 2008 R2. The initial sync worked Ok but since then we have not been able to complete any change syncs. We found out there was an issue with the sync account passwords created by the install and reset one but the other (Sync_) account generated the following error when we try to change it...

"unexpected exception thrown.; Action:PingProvisioningServiceEndPoint, Exception:"

We have also been getting "stopped-extension-dll-exception" in the status in SSM, as well as the following in the EL

ProvisioningServiceAdapter::ExecuteWithRetry: Action PingProvisioningServiceEndPoint, Unexpected Exception: System.Runtime.InteropServices.COMException (0x80010107)
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at System.Management.ManagementObject.Initialize(Boolean getObject)
   at System.Management.ManagementBaseObject.get_Properties()
   at System.Management.ManagementBaseObject.GetPropertyValue(String propertyName)
   at Microsoft.Online.DirSync.Common.PrerequisiteChecks.TryMachineIsDomainControllerCore()
   at Microsoft.Online.Coexistence.ProvisionHelper.IsMachineDomainController()
   at Microsoft.Online.Coexistence.ProvisionHelper.GenerateSyncToken()
   at Microsoft.Online.Coexistence.ProvisionHelper.OpenProxyConnection()
   at Microsoft.Online.Coexistence.ProvisionHelper.InvokeAwsAPI[T](Func`1 awsOperation, String opsLabel)
   at Microsoft.Azure.ActiveDirectory.Connector.ProvisioningServiceAdapter.ExecuteWithRetry(String actionName, Action action).

Any ideas, or can we try to remove and reinstall??