A colleague received the following error message today on an Exchange 2010 server when he tried to set up an Active Sync account (HTTP 401):
Error 401 received from the server, but no authentication methods are supported.
The cause was as follows:
In the Exchange administration console under "Server configuration" -> "Client access" -> "Exchange ActiveSync" the checkbox "Standard authentication (password is sent unencrypted)" was missing.
After the check mark was set, ActiveSync worked perfectly
