Since Arduino 17, many people have been having issues with getting Arduino and Max/MSP communicating. Hans-Christopher Steiner posted a comment in the tutorial How to Set up Arduino and Max/MSP saying that he has released an update, which should sort some bugs out.
Here’s what Hans-Christopher wrote:
The StandardFirmata in 0017 turned out to be kind of buggy, unfortunately. We have things mostly fixed in SVN, but would love to have more testing and bug reports! So here’s a new release. I fixed all bugs that I knew about, including the one where analog pins sometimes acted like they had a log curve on them.
Just download the Firmata.zip and then install the StandardFirmata included in that. I tested this on a Diecimila, I hear there are troubles with the Arduino Pro and others, but I only have the older ones, so testing and bug reports on those are very helpful.
In the Max forum he writes:
The maxuino version should work with Firmata 2.1 as long as the baud/bitrate is set to 57600.
I still can’t try anything myself until I get up and running again with a computer. But if you do try it and it works/has bugs, please post the bug reports and feedback in the comments or directly to Hans-Christopher via his site, which will help him with the testing.