I've done some more experimenting with the Communicator app. It seems like it is working, but I keep getting error messages, too. For example, if I enter the command "display.clear()", the front panel shows "Error code -285 TSP syntax error at line 1 unexpected symbol near ':' query unterminated". The Communicator app also shows ":SYST:ERR? Timeout expired before operation completed." But after the error messages are shown on the front panel, it clears. I can also display text using the display.settext("") command, but I also get the same error messages.
I tried the same commands (and others) using the NI MAX VISA Test Panel window. I get the same error messages and the same behavior.