AP ACH vendor remittance emails hanging up, not getting sent

Hi all

we've been successfully using the ACH functionality within Sage 100 for several months. Lately, we've had some emails hang up the process. During the period when the vendor remittance emails are sent, anywhere from 1-10 emails will not go through and we get an error message like the one attached. I hope you can see it. The error status says:

Error on 'SendMail'
ChikltLog:
SendEmail:
DIDate Jan 19 2012
UnlockPrefix: SBestSoftMAILQ
Username: AP6:sxxxxx
Architecture:Little Endian; 32-bit


Any ideas? thank you in advance