Object reference not set to an instance of an object

Hello !
We are a new in FST and started a game a week ago.
It seems we have some problem and can't understand clearly the cause.
All our users have zero score.
The only have manu logs of FST - but all seems ok except latest
with
Object reference not set to an instance of an object. message inside
and in FST Starter Job we can see
Plugin Trace:
[FST.Plugins: FST.Plugins.StarterWF]
[FST.Plugins (1.0.2.145): FST.Plugins.StarterWF]
Error Message:
Unhandled Exception: Microsoft.Crm.CrmException: The plug-in execution failed because the operation has timed-out at the Sandbox Client.
System.TimeoutException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #C723C668
at Microsoft.Crm.Sandbox.SandboxCodeUnit.Execute(IExecutionContext context)
at Microsoft.Crm.Workflow.Services.ProxyCustomActivity.Execute(CodeActivityContext executionContext)
How to check us4.fantasysalesteam.com link is available with user & password ?
Does anyone could advise us where to dig ?
Thanks,
Alex