Prevent event creation on server-side

I’m using dhtmlScheduler v3.0 and java connector on server-side.
In some cases, when user is creating, updating or deleting events I can forbid this action.
I mark this action as invalid or error and everithing is fine on the server-side. But client-side executes my action despite the fact that request returns error. How I can prevent executing action on client-side, when server returns error?


Client side will not revert values back, but deleting for example will be blocked for sure.
You can attach client side helper for dataprocessor on onAfterUpdate event and if action response is error or invalid to something with event in question ( set different color for it, for example, or change its date|text )