Maybe I'm just being pedantic, but the commands specified by the manufacturer could be interpreted as two 32bit words, four bytes, or eight ASCII characters.

If the commands work intermittently, then I suspect that there is a timing issue. This could be caused by specifying the wrong carrier frequency or repeat timing, if the device wants commands to be repeated. I've also seen some devices want commands followed by their compliment.

The above does not exhaust the list of potential complications. As Duct Tape and Ernie suggest, we need more info. How did you learn these commands?

You could also have some IR interference.