If you have password policies that support non-ASCII passwords or that require passwords to be 4 characters or shorter, or 12 characters or longer, make sure you select the Attach common proxy user to common proxy policy option (the default setting) on the OES proxy install screen.
Selecting this option prevents the password-compliance issues with the proxy user after the installation.
If you are installing, then abort the installation and reinstall OES. In the common proxy page, you must provide a password for the common proxy user that complies with your password policy.