Yes - same problem - I wish someone could tell me whats wrong.
I would greatly appreciate any troubleshooting help with this irregular fax transmission problem.
I have no problems faxing with my old XP system. Let that serve as the baseline for my fax capacity.
I have a new Windows 7, which I outfitted with a USB fax/modem adapter and with which I use the included Windows 7 fax utility. Sometimes it functions. Sometimes. And sometimes it works partially. Today, for example, I faxed 10 documents to 10 different recipients. A few of the faxes went through normally, then all of the remaining faxes failed. When they fail, the pattern is like this: the fax utility dials, the recipients fax picks up at 20-30 seconds, and precisely three seconds later, the faxes terminate with the details that the utility encountered "an unexpected error". Multiple redials achieve the same failure, although one or more along the way may pass through successfully. I have looked for patterns and have found none.

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