To enable the automatic client upgrade feature two XML keys must be used at minimum: <CurrentVers> and <BuildCSUpgradeable>. BuildCSUpgradeable must be set to "True" and CurrentVers must be set to be any number greater than the previously installed version.
It is important to note that even if CurrentVers was not set in a previously installed application the default value is 1. Because of this default value it is possible to implement the automatic client upgrade feature in a new application release even if previous releases did not support this. Simply increment the CurrentVers to 2 and the automatic client upgrade can occur for older clients.
For more information about the automatic client upgrade feature see Technical Note 07-22, Building Applications with 4D 2004: Automatic Client Upgrade