B2B Message Not Reaching Partner

Hi

I am sending data from RFC to My partner(AS2) . when I look into the message log I notice that the message

has been delivered .and I am getting 997 acknowledgment

But my partner says that they have not received the message, I have given the correct URL,sender and receiver id

what might be the issue is there any way to track the AS2 message apart from the communication channel

I have attached the screen shot of acknowledgment

Note: we are using B2BAddon

Thanks

Jai