When trying to logon a few times in a row I get a Internal Server Error as shown in the attachment (error.jpg). It does not make a difference if the user is a local liferay user or an AD/LDAP user. The steps I took:
1. Logon with a local user (admin or not, this makes no difference)
3. Logon within seconds after logout
4. Internal error occurs
This issue only occurs when using Internet Explorer 9.