From 4.523 DP4 has significant enhancements to its networking facilities. In order to implement this there are some changes to the mechanism used for communication between applications and the database manager : applications now pass an additional "server handle" to the database manager. In order to maintain the maximum compatibility between DP4 releases this has required changes to usrlibt.dll, which is used for the communication. Applications built for the new release will complain about missing ordinal 20 in usrlibt.dll if the new version is not installed. The new usrlibt.dll can be installed on any 4.520 or later release, and will work without any problems - older versions will simply ignore the additional information. Older applications calling new components will be given a default value for this handle.