After a Post Office was pdated from 18.1.0 to 18.2, Webaccess users of the updated post office get a 9505 error logging in :
 Your post office is unavailable. The post office Agent might not be configured for SOAP. Please contact your system administrator.
The 9505 Webaccess error was resolved by updating the Webaccess code from version 18.1.0 build 132269 to Webaccess 18.1.1 build 133172 ( or to Webaccess 18.2 ).