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=76208.40
Closing and re-opening/re-initializing the port would probably be a better solution. But disable is simpler and works.
And works??? For what? Permanently disabling a perfectly good BFL single, just because there was some hiccup somewhere for a brief moment?
We seem to have a disagreement on the definition of "works" vs. "issue".
J/K. Ckolivas is a god.