iMessage not working (but SMS relay is)

I recently upgraded from Mavericks to Yosemite, and Messages (which I use for iMessage) was working as expected. Then, randomly, it stopped working yesterday. Any time I attempt to send an iMessage from my MacBook Pro Retina, it results in a red "not delivered" message. However, SMS Relay IS working. The only potential culprit I can think of is that I recently reset my default keychain password. But I'm fairly certain Messages was still working for a time after doing this. Any help or tips would be greatly appreciated!

So far I've tried:

- Signing out and then back in (using my Apple ID in the Messages app)

- Restarting

- PRAM reset

And am seeing the following console errors when I attempt to send:

(have removed personal info, such as IDs)

- 10/24/14 9:59:23.527 AM imagent[359]: [Warning] callerURI - No bindings !!

- 10/24/14 9:59:23.531 AM imagent[359]: [Warning] Request to send message: IMMessageItem[outgoing: YES sender=(null); service=iMessage; handle=+16185582383; unformatted=(null); country=US; roomName='(null)'; flags=100005; subject='<< Message Not Loggable >>' text='<< Message Not Loggable >>' messageID: date:'' date-delivered:'0.000000' date-read:'0.000000' date-played:'0.000000' transfer guids: '(null)' empty: NO finished: YES sent: NO read: NO delivered: NO audio: NO played: NO from-me: YES DD results: NO DD Scanned: YES Downgraded: NO emote: NO expirable: NO expire-state: 0 error: 0] to chat: IMDChat: GUID: iMessage;-; [phone number I was sending to] Style: - State: 3 Participants: (

"[IMDHandle: <[phone number I was sending to]:(null):US>]"

) Room Name: (null) Display Name: (null) Identifier: [phone number I was sending to] Unread count: 0 Row ID: 29 Group ID: from NIL ID fromAccount: IDSAccount: [Service: com.apple.madrid User: ID: Type: Apple ID Active: YES Registration Status: Registered]

- 10/24/14 9:59:23.532 AM imagent[359]: [Warning] Group message controler failed to prepare chat: IMDChat: GUID: iMessage;-; [phone number I was sending to] Style: - State: 3 Participants: (

"[IMDHandle: < [phone number I was sending to]:(null):US>]"

) Room Name: (null) Display Name: (null) Identifier: [phone number I was sending to] Unread count: 0 Row ID: 29 Group ID: error: 4