The spaces in your log message makes the command wrong.
* Slot-1 SWTCORE1.2 # create log message test 123
^
%% Invalid input detected at '^' marker.
* Slot-1 SWTCORE1.3 # create log message "test 123"
* Slot-1 SWTCORE1.4 #
However, using a variable inside "" does not seem to work.
Slot-1 SWTCORE1.5 # set var port "1:1"
* Slot-1 SWTCORE1.6 # show var port
1:1
* Slot-1 SWTCORE1.7 # create log message "test port $port"
* Slot-1 SWTCORE1.8 # sh log
03/13/2018 10:07:40.37 Slot-1: test port $port
Using _ instead of spaces and not use quotes makes it possible to use variables but is a bit ugly.
* Slot-1 SWTCORE1.14 # create log message test_port_$port
* Slot-1 SWTCORE1.15 # sh log
03/13/2018 10:10:35.50 Slot-1: test_port_1:1