Citrix client connection failure due to Access Gateway service failure

I have a problem with a Citrix Access Gateway that controls access to my two Citrix PS4.5 serves. Prior to yesterday afternoon all was fine and has been for at least a few months. Then the clients could not connect to the Citrix Servers via web browsers which would return an HTTP 500 internal server error. The clients connect to a Windows 2003 SP1 server with IIS 6 installed, running the Citrix Access Gateway Advanced Edition (version 4.5.2.0) either internally or through a Citrix Access Gateway appliance if theyre external. The appliance has this server configured as an endpoint but the log shows that it cannot connect to it. The server has all Citrix services running except for the Citrix Deployment Server service which starts and then stops immediately. The following error appears in the event log after it has stopped.
Event Type:      Error
Event Source:      CtxMsamDeployment
Event Category:      None
Event ID:      0
Date:            25/04/2009
Time:            12:13:49
User:            N/A
Computer:      FILESERVER
Description:
An error occurred while starting the service. The required setting 'DeploymentSchedulerInterval' cannot be loaded.

Im unable to get into the Access Gateway Server Configuration Tool, presumably because the service is stopped. The domain account the service runs under has not been changed and the other Citrix services also run under this account without a problem. I have checked the ODBC connection to the Access Gateway database running on a separate SQL 2000 server and it connects fine. Needless to say I have rebooted both the Gateway server, CAG, both Citrix servers and the database server to try and clear the problem.

There are also a number of COM+ errors in the event viewer which occur when the gateway is accessed. Here is the error-

Event Type:      Error
Event Source:      COM+
Event Category:      (98)
Event ID:      4826
Date:            25/04/2009
Time:            12:59:01
User:            N/A
Computer:      FILESERVER
Description:
A COM+ service (such as Queued Components or Compensating Resource Manager) failed an ApplicationLaunch event.  If this problem continues, try disabling CRM and/or QC on your application. If you are using QC, make sure that Message Queuing is installed. The service GUID and HRESULT are: {666F1874-46B6-4149-BD55-8C317FB73CC0}

Server Application ID: {666F1874-46B6-4149-BD55-8C317FB73CC0}
Server Application Instance ID:
{21A1B9A0-339C-4A04-B6B7-61ADDD73AD83}
Server Application Name: Access Gateway Server
The serious nature of this error has caused the process to terminate.
Error Code = 0x80131534 :
COM+ Services Internals Information:
File: d:\nt\com\complus\src\comsvcs\srgtapi\csrgtserv.cpp, Line: 322
Comsvcs.dll file version: ENU 2001.12.4720.2517 shp

The same error occurs when trying to start the Access Gateway Server component in Admin Tools\ Component Services.

Im going to try restoring the Citrix system files and registry from the last backup to see if this will get things working but if anybody has any ideas how I can get this back to a working configuration quickly, Id be very grateful.

Thanks for your help