Problem with online backup of some hg files

[Andrew Gillett]

I use Mozy online backup. After the recent Windows 10 1803 update, it 
fails to back up some files in .hg folders, giving the error "Unable to 
open file for backup". The only pattern I can see is that all of the 
files that fail to back up have the extension i, d, or are named 
"requires". However, some.i and .d files do back up successfully.

I've been in touch with Mozy support – they are suggesting it's either 
some issue with file permissions (but the files affected have normal 
permissions), or with distributed COM errors that show up in my Windows 
event log. They've told me to contact Mercurial support. Personally I 
can't see any reason why the affected files can't be backed up – is 
there anything special about these files or their permissions that I'm 
not aware of?