Can't send files with OS X 10.9 Messages.app

Hi,

I upgraded from Lion to ML, and I was using Messages BETA in Lion before the update. Back in 10.7, I was able to send files (pictures mostly) with Messages to any other iMessage available contact.

After the update to Mountain Lion, I can't send files any more, and have a lot of log entries about it:

20-08-12 21:49:21,447 Messages[252]: [Warning] -[ChatTranscriptViewController _increaseResourceLoadCountForURL:] url called for url: ichat-resource://coreui/exclamation-pressed with nil _loadingIdentifiers
20-08-12 21:49:23,337 com.apple.imfoundation.IMRemoteURLConnectionAgent[293]: [Warning] Denying xpc connection, task does not have entitlement: com.apple.private.imcore.imremoteurlconnection  (IMTransferAgent:292)
20-08-12 21:49:23,337 com.apple.imfoundation.IMRemoteURLConnectionAgent[293]: [Warning] Denying xpc connection, task does not have entitlement: com.apple.private.imcore.imremoteurlconnection  (IMTransferAgent:292)
20-08-12 21:49:23,338 com.apple.imfoundation.IMRemoteURLConnectionAgent[293]: [Warning] Denying xpc connection, task does not have entitlement: com.apple.private.imcore.imremoteurlconnection  (IMTransferAgent:292)
20-08-12 21:49:23,339 com.apple.imfoundation.IMRemoteURLConnectionAgent[293]: [Warning] Denying xpc connection, task does not have entitlement: com.apple.private.imcore.imremoteurlconnection  (IMTransferAgent:292)
20-08-12 21:49:23,339 com.apple.imtransferservices.IMTransferAgent[292]: [Warning] Remote loader crashed for request: <NSMutableURLRequest http://init.ess.apple.com/WebObjects/VCInit.woa/wa/getBag?ix=1>
20-08-12 21:49:23,340 com.apple.imtransferservices.IMTransferAgent[292]: [Warning] Bag loading failed! Error (__kIMRemoteURLConnectionErrorDomain:-1): No se ha podido completar la operación (error __kIMRemoteURLConnectionErrorDomain -1). (null)
20-08-12 21:49:23,341 com.apple.imtransferservices.IMTransferAgent[292]: [Warning] Remote loader crashed for request: <NSMutableURLRequest http://init-p01md.apple.com/bag>
20-08-12 21:49:23,341 com.apple.imtransferservices.IMTransferAgent[292]: [Warning] Bag loading failed! Error (__kIMRemoteURLConnectionErrorDomain:-1): No se ha podido completar la operación (error __kIMRemoteURLConnectionErrorDomain -1). (null)

The file transfer window in Messages shows "0 of XX KB sent" for all the files that I send, but at least I can recieve files from other iMessages available contacts.

I also followed this hint without any luck so far: https://discussions.apple.com/thread/4142706?answerId=19224592022#19224592022

Does anyone knows how to solve this?

Regards,