furthermore I found these 3 error messages on event viewer :
1-Web service request ListExtensions to Report Server crm/.../ReportService2005.asmx failed. Error: The request failed with HTTP status 503: Service Unavailable.
2-Report Server Windows Service (CRM) cannot connect to the report server database.
3-CrmTrace encountered an error. Additional Info:Error in LoadDeploymentSettings [Cannot open database "MSCRM_CONFIG" requested by the login. The login failed.
Login failed for user 'NT AUTHORITY\NETWORK SERVICE'.], Stack Trace : at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
at System.Environment.get_StackTrace()
at Microsoft.Crm.CrmTraceSettings.Load(String traceDirectory)
at Microsoft.Crm.CrmTrace.get_RefreshTrace()
at Microsoft.Crm.CrmTrace.Write(Guid orgId, TraceCategory traceCategory, TraceLevel traceLevel, Int32 skipFrames, String format, Object[] args)
at Microsoft.Crm.CrmTrace.TraceFormat(Guid orgId, TraceCategory traceCategory, TraceLevel traceLevel, String format, Object[] args)
at Microsoft.Crm.CrmTrace.Initialize()
at Microsoft.Crm.Asynchronous.AsyncService.StartServiceComponents(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
at System.Threading.ThreadPoolWorkQueue.Dispatch() (Reporting Process:CrmAsyncService, AppDomain:C:\PROGRA~1\MICROS~4\Server\bin\)
I checked "NT AUTHORITY\NETWORK SERVICE" access right and it has "Owner", "CRMReaderRole" & "public" access rights to "MSCRM_CONFIG" and "ORG_MSCRM" databases.