This happens to me occasionally as well (Win7/64 here), typically once every day or two. Happens in cgminer 2.4.1 and 2.4.2; in the cgminer window the device's hashrate is listed as 'OFF'.
This never happened with 2.3.6; I ran that version for 2 weeks straight without any issue. So I'm also leaning toward it being a cgminer issue introduced in 2.4.1.
In 2.4.1+, devices are disabled (rolling rate is "OFF") when scanhash() returns 0. Check your cgminer log for reasons (all error conditions log error messages). I don't think it is an "issue". What's the point to have a device that cannot hash.
cgminer just handles errors coming from the device and disables the device. That is its error handling.
See nedbert9 post:
https://bitcointalk.org/index.php?topic=76208.40Closing and re-opening/re-initializing the port would probably be a better solution. But disable is simpler and works.
I'll check into the logs tonight to see if they have any further clues ... I don't have any evidence (only observation and comparison to earlier behavior) to know what the root cause of the scanhash() failure is.
I do know that my Singles hashed for 2 weeks solid under 2.3.6 without any failure. Those same Singles have now had 1-2 'OFF' failures every day or two for the past two weeks running 2.4.1 and 2.4.2 in the same environment (same ambient temperature, same host PC, same USB hubs, same cables, same physical location and position).
That observation, plus several posts from other Single users running 2.4.1+, make a reasonably strong case to at least suggest that something may be broken in 2.4.1+.
I've read nedbert's post that you referenced; he is encountering the same problem as being described here. The point is that prior to 2.4.1+, Singles did not spontaneously 'stop hashing'. So I am trying to understand why they would be doing so now ... and, so far, the circumstantial evidence seems to be pointing the spotlight on cgminer 2.4.1+.
I have one Single working now under CGminer 2.4.2 and before 2.4.1 without any problems, but I use Windows Server 2003