OK, last night I managed to get my analog sub-circuit simulating. Not without overcoming a few hurdles though. First off, the ISIS help topic for creating Sub-Circuits is spars to say the least. It doesn't even provide a sample schematic of a circuit that the sub-circuit rectangle represents. My sub-circuit rectangle represented a simple analog circuit but the "Ports" selection provide Input, Output, Power, Ground, Bi-Directional and "Default" choices with no clue which to use. I discovered from trial and error that "Default" Ports should be used for analog circuits, even GND and Power.
Here's an important tip:
The first step in creating a Sub-Circuit is to place a Sub-Circuit rectangle on the pallet of your main schematic. This pallet is called the "Parent Sheet". The sheet that will contain your actual sub-circuit is called the "Child Sheet". Prior to accessing the Child Sheet to draw your schematic you must do the following.
(1) Right click the rectangle and select "Properties".
(2) Fill in the "Name" textbox with a descriptive name of your subcircuit.
(3) Fill in the "Circuit" textbox with a component identifier label that's not currently in use in your main (Parent Sheet) schematic. For instance if you already have U1, U2 and U3 on your pallet fill in the "Circuit" textbox with "U4". Without the quotes.
Please note that the "Circuit" textbox will already be filled with a default text. I you don't change it now you never will be able to after opening the Child Sheet! I tried changing the default ("CCT001") to something more appropriate ("U1") and my subcircuit schematic on the Child Sheet VANISHED!
By the way. Since the Sub-Circuit help topic was so sparse I navigated to
YouTube where I found this. There's no audio but it's still a 1000 times better than the help topic.
https://youtu.be/Oc1lQYWFoGQ
Chris