PL/I for MVS & VM and Enterprise PL/I share the same set of run-time messages, and this can lead to messages that should be read with understanding and flexibility. For example, when the run-time issues a message for UNDEFINEDFILE in an Enterprise PL/I program, the message will mention both MVS and VM constructs even though Enterprise PL/I does not currently support VM. The meaning should be clear nonetheless.
Also, if you compile with the compiler GONUMBER option, the run-time messages will refer to a "statement" where your exception has occurred. This "statement" is, for Enterprise PL/I, the line number in the source program of the statement that raised the exception.
Finally, the format and content of run-time messages are different under the Language Environment run-time than under the OS PL/I run-time. You can find complete descriptions of the run-time messages in z/OS Language Environment Run-Time Messages.