If you direct a command to an incompatible system, you might encounter an error if the directed command includes a keyword that is unknown on either the local system or the remote system. For example, if you include a new keyword with a command issued on a higher level system and direct it to a lower level system, the command will fail on the lower level system where the keyword is unknown. In addition, if you include a new command keyword with a command issued on a lower level system and attempt to direct it to a higher level system, the command will also fail on the lower level system where the keyword is unknown, and the command will not be sent to the higher level system.

Similarly, if you use custom fields and you attempt to direct a command that includes a custom field keyword, the custom field must be defined on both the local and remote systems. If the custom field is not defined one of the systems, the command will fail on the system where the custom field is undefined because the custom field keyword is unknown. (For information about custom fields, see Defining and using custom fields.)