I get the same problem with Linux sometimes.
We have an old fileserver that provides an NFS file system for our Windows machines. I’ve noticed that sometimes it is very slow — say for example I copy a large directory from one location to the other; it may look like the directory was actually deleted for a minute or two.
When using Multi-Edit, it sometimes cannot write to a file. There is a similar message to what you guys are reporting. But when I look in the NFS directory, there are a series of temp files created that contain the changes I was trying to save.
I also get a similar problem with a java program I have as well. It can create a directory on this Linux fileserver but cannot always create a file on it. I think that it is related to this NFS filesystem, so it may not be a problem with Multi-Edit.