All sent messages or only one?
If all, check your SMS settings. (Call your provider's tech support for help with that.)
If only one, the address may be bad, the receiving mailbox may be full, the receiving email server may be down.
At any rate, after about 5 days (it depends on your email provider's settings) the message will stop trying to send and it'll disappear. (You'll probably get an email from the email daemon that the message couldn't be delivered because of <some code number> <some English explanation of what the code means>.)