Any C-Max instructions that specify an input or output, or a message number in the case of a serial bobcat, first needs to have that module defined in the project System Map. Look for "System Map" under the "Project" menu and then define your module type at the appropriate module address (define all your modules and any slave controllers). The different Bobcats are defined with names like "BOBCAT-A" where:

-A = ASCII bobcat
-T = Temperature bobcat
-H = Humidity bobcat
-L = Light sensing bobcat

Once this is done you will then be able to select the input/output/messages in C-Max when programming. Always save and load your entire project when programming, not just the program.