Outlook 2007 Cannot connect to Exchange 2003 via RPC over HTTP
If you are facing issues to get Outlook 2007 to connect to exchange 2003 server over RPC, you may try the following:

Changes to be done at the Outlook client

• Click Start, click Run, type regedit in the Open box, and then click OK.
• Locate and then click the following subkey: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\RPC
• On the Edit menu, point to New, and then click DWORD Value.
• Type DefConnectOpts, and then press ENTER.
• Right-click DefConnectOpts, and then click Modify.
• In the Value data box, type 0, and then click OK.
• Exit Registry Editor.

Exchange 2003 OWA Forbidden error

• For OWA to function correctly, please ensure that all permissions are enabled / "selected" for the exchange virtual folder
• This can be done by right-click on the folder > Properties >Virtual Directory tab

TIPS while trouble shooting DNS errors

• Make sure you are able to ping the server (IP or hostname)
• Flushdns many a times helps to clear the cache and ensure your changes are reflected
• Ensure that you restart the DNS services after making changes in the DNS
• Check the physical network before you start making changes ot DNS

Exchange OMA error ""Collection was modified. Enumeration operation may not execute"
Please follow the below steps. Please note that you need to restart IIS after each task

• Ensure you have the same asp.net versions in both Microsoft Server ActiveSync and OMA virtual folder
• Add a NetBIOS name as host header value for the defualt website
• In exchange system manager - Servers -> servername -> Protocols -> HTTP -> Exchange Virtual Server -> Properties -> Settings Tab
• Enable Form based Authentication -> Compression -> None and Changed "None" to "High"
  

If you need further assistance, please contact us at support [at] velaninfo.com