Added more descriptive error

lib/apex/frame/immutable_entity.rb

@@ -14,7 +14,7 @@ module Apex
       raise ArgumentError.new("callsign must be a String") if not callsign.kind_of? String
       raise ArgumentError.new("ssid must be an Integer.") if (not ssid.nil?) && (not ssid.kind_of? Integer)
 
-      raise ArgumentError.new("ssid must be a value between 0 (inclusive) and 15 (inclusive): #{ssid}") if (not ssid.nil?) && (ssid < 0 || ssid > 15)
+      raise ArgumentError.new("ssid must be a value between 0 (inclusive) and 15 (inclusive): #{callsign}-#{ssid}") if (not ssid.nil?) && (ssid < 0 || ssid > 15)
       raise ArgumentError.new("Callsign can not be an empty string") if callsign.empty?
       raise ArgumentError.new("Callsign must only contain numebers and letters") if callsign.strip.match?(/[^a-zA-Z0-9]/)