Thank you for your post. Take a look at this KnowledgeBase article. If you look at the bottom of the page, you will see that when reading a command through the NI-488.2 Communicator in MAX, the applet scans for any character that seems to be binary data. The alphanumeric, carriage-return, and line-feed characters are not considered binary data. Thanks again for your post, and feel free to post again if you have anymore questions!
In order to send a CR or LF, you can of course use the constants from the string palette. You can also use \r or \n as long as you right click on your string control/constant and select '\' Codes Display. If you don't take this basic step, all that you are sending is the separate characters '\' and 'r'. Beginners often make this mistake and there are numerous threads on this subject.
p.s. You might want to start using VISA instead of the low level GPIB functions. VISA is more portable and is the recomended API.