Q: why can't i send an imessage or sms to one particular contact?

Hey Susannah_C,

Thanks for the question. I understand you are unable to message a specific contact. The following resource provides troubleshooting information for this symptom:

If you still can't send or receive an iMessage, follow these steps

 

1. Make sure that the contact trying to message you isn't blocked in Settings > Messages > Blocked.

 

2. Make sure that the contact you're trying to send a message to is registered with iMessage.

 

3. If the issue occurs with a specific contact or contacts, back up or forward important messages and delete your current messaging threads with the contact. Create a new message to the contact and try again.

 

4. If the issue occurs with a specific contact or contacts, delete and recreate the contact in the Contacts app. Create a new message to the newly created contact and try again.

 

5. Back up and restore your device as new.

iOS: Troubleshooting Messages

http://support.apple.com/kb/TS2755

Thanks,

Matt M.