Offline WSUS - clients won't get updates (export and import updates)

We have got two WSUS servers, one is connected to the internet while the other is inside a closed network (due to security). we are using import-export in order to sync the update from the online server to the offline server.
The problem is that after approving a test machine, setting the GPO and checking for new updates nothing happen, the client log reported: "0 updates detected" (full log in RED below), 


Solution: after copying c:\wsus folder from the external server to internal server, exporting and importing (again) the database > clients can get updates.


How to perform export using WSUSutil.exe:


1 ) from external machine open command line and go to %drive%\Program Files\Update Services\Tools folder and type


wsusutil.exe export export_package.cab logfile.log


2) copy the c:\wsus folder to the internal server.


3) copy export_package.cab to the internal server (you don't need to copy the logfile.log)


4) on the internal server run:
wsusutil.exe import export_package.cab logfile.log






/////////////////////////////////////////////////////////////

2011-09-15	11:38:55:181	 380	150c	Agent	*************
2011-09-15	11:38:55:196	 380	1044	AU	>>##  RESUMED  ## AU: Search for updates [CallId = {32CCAA2B-1A4D-4846-9C51-7F54E9A2E42F}]
2011-09-15	11:38:55:196	 380	1044	AU	  # 0 updates detected
2011-09-15	11:38:55:196	 380	1044	AU	#########
2011-09-15	11:38:55:196	 380	1044	AU	##  END  ##  AU: Search for updates [CallId = {32CCAA2B-1A4D-4846-9C51-7F54E9A2E42F}]
2011-09-15	11:38:55:196	 380	1044	AU	#############
2011-09-15	11:38:55:196	 380	1044	AU	Successfully wrote event for AU health state:0ts.