Email Log Failed (Error with sending data; socket error)

SyncBackSE V6.5.4.0
Windows 7 Pro, 64-bit, current on Windows updates

I've been using SyncBackSE for over a week and really like it. All of a sudden I've got issues emailing the log. The backup completes, but I get the error shown in the subject.

I have 2 almost identical backup jobs. The only difference between the 2 is the destination. On one of them it's local (a 2nd hard drive on my PC) and the other is on the network (to a server). They each run 5 days a week 30 minutes apart. Both ran fine for over a week, then the network one started getting this error, while the one to a local hard drive was fine. I did a "Test email" from the failing job and it worked just fine, so the settings are OK.

I thought maybe something got corrupt in the network backup job. So I deleted it, copied the local one to make a new network job, and changed the destination on this new network job to the network folder. Still would fail with this error. The local backup job still ran fine.

Then last night, for the first time, the local one got the same error. I rebooted (hey, it IS windows, after all) and that did not help.

I found the postings from 2012 about strange socket error. The recommendation was to use the new version, then in beta, but I'm way past that version so I assume it does not apply.

Ideas? Suggestions?

Thanks.