[s] or [send] only takes one argument: the name of the send/receive pair. You have more than one argument (so there’s a space after your first argument). To use multiple-word descriptors, try

[s my_message]

or
[s "my message"]
…not sure if quotes work for this, but they do in other places like naming subpatches…give it a go ;)

The message appears multiple times because you have the error in multiple [s] objects. If you click the error in the Max Window and then click "Show Object" at the bottom, it will highlight the culprit.