My guess is that the file size is too large, there is a 2MB limit on attached files. You can either compress it further to make is smaller (which will also reduce the fidelity) or you can truncate it. High quality MP3's do tend to take up about a meg/minute-ish.
On your zoom, if you're getting MP3's, you've either got iTunes set up to convert to MP3 upon import or you've got the zoom set to record in MP3 format. I would suggest switching to 44.1 linear on the recorder and doing the conversion in iTunes if that's not already what you're doing.
I just traded up my H4 for an H4N and I really like it. $300 gets you a lot of recorder these days!