Problem with OWA, HTTP/1.1 503 Service Unavailable on exchange server itself and from OWA

I am trying to access my server using OWA
My OWA server sits in a different domain, but this works for all domains so I suspected it was this particular exchange server. On the server itself I have tried to open http://servername/exchange and it prompts me for a user name and password (which is strange as im logged in as the domain administrator for this domain). I type in the information and it comes back with the following error

HTTP/1.1 503 Service Unavailable

The same error I get from the main OWA server for the forest.

I am running windows 2003 server SP2 with exchange server standard SP2.

I have had this issue for several weeks and just cant understand why this does not work
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Glen KnightCommented:
Are there any EXCDO errors in the Application Event Log with ID 8206?
Make sure hotfix is applied:

Look for event log entries relating to not being able to update a calendar entry.
Have a look at: to obtain the HKCRScan tool.
Have a look at the last few entries of this thread:
Once you have the HKCRScan tool you can run hkcrscan > c:\output.txt

Scroll to the end of the text file of the output and it will give you a registry key name that exceeds the 259 charactler length.

Export this key to back it up then remove it, restart the exchange services and your problem will be resolved.

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when accessing the OWA web site the administrator ID will not work.  you must use an ID which has an associated email account whcih Administrator especially the domain admin accoomy generally does not.  Please try to access OWA with an ID that has a valid exchange mail box and let me know if it works.  please also provide the complete web address used from anywhere in your network.  In addition can you get to this prompt from an web address outside the domain on the internet
the ExchangeApplicationPool in IIS is most likely offline
start the application pool and monitor the application log for errors that may be causing it to go offline
RPUKsupportAuthor Commented:
I ran the hkcrscan tool, found the key, deleted it, works like a charm.

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