I've gotten that when I hit "send" but the name was misspelled, or I didn't have a subject line, or didn't have a message. I don't think it will let you send a blank message. (yes, I've accidentally done all of these things at one time or another. lol)
There may be other causes, but those are the ones I know of.
You and I are on the same thought process in that case. Unfortunately, I could find nothing wrong in any of those cases. I even checked the message for misspelling, punctuation mistakes, and grammatical errors. Still wouldn't go through
Something is going wrong the array is a php error. No way for me to know. Does the recipient have a name with special characters? Are you posting links or special characters?
Recipient has no special characters. I did try to post a link, but I removed it in case that was the problem. No luck. I've tried probably about 20 times. I even deleted the whole thing and started over just to see.