I don’t think the Internal works that well for some Mainframes. If you have enterprise, you may escalate this to technical support. Contact Technical Support
Or just don’t use Internal
I’m more familiar with using the Mainframe from the emulator that is installed on the machine.
I’m most accustomed to using the “IBM EHLLAPI” provider when your emulator doesn’t have a specific provider for it. However, you may work with technical support for getting a provider for your emulator.
To use the EHLLAPI, find the hllapi DLL file in your emulator’s program files folder where it is installed, and that usually will get it connected. There could be other issues though, but I guess you’ll see. Since it attaches to an existing session (such as ‘B’ session), I believe you would need to use Start Process or Open Application prior, especially if you have a separate profile configuration file that is opened like mine is (which you would use as the Argument in the Start Process.