IBM z/OS 2.2 PTF requirement
The following issue with the IBM z/OS 2.2 operating system affects Horizon TCP/IP:
An EZASMI CANCEL of an outstanding SELECT completes with Rc=0 and ERRNO=0 but does not CANCEL the SELECT call.
If you use Horizon TCP/IP for sending and receiving between Model 204 applications, you will need to apply IBM PTF UI34846. Without this fix, TCP/IP client connections for Model 204 cannot be initiated.