Sugar CRM Version 4.2.1d

We are experiencing an error when certain users attempt to send and email to certain addresses. When hitting send an error similar to the following will appear:
bean not found by id: 1928b8b6-44e2-6ced-881a-4562219f4b9c

when this same user sends the same content of the email (the content can be as simple as test for the subject and test for the body of the email) to another address it will go through

The address that the user gets the error on can be sent to by another Sugar user.

Recap:
User 1 (U1) can not send to address 1 (A1) however can send the same message to address 2 (A2)
User 2 (U2) can send the A1 and A2 without a problem