When you try to access the ECP in exchange 2010, in your web browser you see ERROR 400 BAD REQUEST. See the image below. Ive seen this on new installs of exchange 2010.
This is down to the security on the OWA virtual directory and the ECP not matching, the quickes way to fix this is to regenerate both virtual directories. Use the commands below to do so.
Open the exchange managment shell and enter the below.
Remove-OwaVirtualDirectory -Identity "owa (default Web site)"
Remove-ECPVirtualDirectory -Identity "ecp (default Web site)"
This will have recreated both OWA and ECP virtual directories, you will be able to login to the ECP now.
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