The AMX ICSP does not permit more than one ICSP File transfers at any given time. Certainly, you can have any number of different panels connected to an AMX system only limited by the capacity of the AMX system.

Here is an overview of how TPControl works:- 

When attempting to connect to an AMX System, TPControl opens an ICSP connection using a dynamic Device ID e.g. 32001 or similar. It does this specifically to determine if the AMX system has a BYOD license. So, if the system_license.tpc exists, that file is retrieved via AMX ICSP file transfer so that TPControl can interrogate the credentials and determine if the BYOD license is valid for that AMX system.

NOTE: this happens extremely quickly, over a few milliseconds.Then, accordingly, TPControl will interrogate if there is a file named system_license.ui (or system_license.tp4) on the AMX system and if so, determine if it is a newer UI file than TPControl already has if previously retrieved from the AMX system and if not will commence another ICSP File transfer to retrieve that file, and the ICSP File Transfer terminates at completion 

NOTE: If the BYOD file does not exist, no ICSP File Transfer is formed and TPControl then queries via HTTP/HTTPS if there is a BYOD UI file hosted on TPCloud for the relevant BYOD license and if so TPControl downloads via HTTP/HTTPS the relevant file (this is a NOT an ICSP File Transfer).

At completion of a UI file transfer which TPControl will process then reform the connection process, TPControl ultimately forms an ICSP connection using the Device ID defined in the current active TPControl profile e.g. 11001 or similar, depending on your settings.***

So, the warning notification you attached earlier; "The control system is busy with a file transfer. (Code 4)" relates to TPControl identifying that the AMX System currently has an active ICSP File Transfer or in the case a previous transfer experienced a problem the AMX Connection Manager can take up to 90 seconds to terminate (or release) and therefore permit any subsequent ICSP File transfer requests.

Questions to potentially remedy/avoid persistent recurrences of the warning;

1. Are you hosting a system_license.ui (or system_license.tp4) file on the AMX System or in TPCloud?- If your answer is the "AMX System", we strongly recommend that you consider hosting the BYOD UI file in TPCloud for the relevant AMX Systems Token.The primary benefit being that it avoids most problems associated with AMX ICSP File transfer warnings, as UI retrieval occurs directly between TPControl and our server (not the AMX System) via HTTP/HTTPS as well as improved bandwidth (limited only by Internet and our server load at the time of retrieval. In practice, TPCloud retrievals are much faster than over AMX ICSP File Transfer.- 

If your answer is "TPCloud", We would ask;

2. What is the Model and Firmware version of the AMX control system? Ensure it is running current firmware.