Maybe the file(s) were being updated at the exact instant?
No there is a sender/receiver file locking protocol to prevent that problem, or it would be a constant source of pain. All of ACP's file-reading weather servers lock the file, as does the source of data (e.g. Boltwood or AAG) before reading or writing. It's probable that someone else had the file locked and didn't let it go "for a while" (there is a limit in the ACP weather server!). Post/attach the SRO weather log file which is in the usual place My Documents\ACP Astronomy\Logs and is named with the date in the name. Then I can say for sure.

This infernal system of loads of people locking/reading/unlocking a file is not a good solution. A few months ago at my suggestion SRO set up a web based weather/roof status delivery system which provides JSON (machine readable) data. Then I wrote a newer ACP weather server to use this HTTP/JSON feed. This system avoids all of the problems of Microsoft folder sharing and file locking.

At present SRO is undergoing some management and infrastructure changes and as a result the new ACP/SRO weather server hasn't been given to their customers. I don't want to do it because I don't know where they are going with their roof control system and weather. So for the moment you'll just have to endure the occasional glitch. In any case, this is an issue for you to discuss with SRO.