Mac OS X accessing Windows Share Strange thing keeps happening with one of my clients. They are running 3 iMacs 2of which are running 10.9.3 and 1 is running 10.9.4. While they are accessing a Windows share, they can be working away quite happily until it comes to saving where they no longer have access to the file opened from the server and have to save as a new file. They are accessing using smb://{servername}/{share}

What would cause this?

Cheers
Apple moved to SMB2 in Mavericks.  There have been many reported issues regarding Macs using SMB2 to access Windows shares.  There's even a site dedicated to this specific set of issues!

For a dated, but good explanation of work-arounds see this ZDNet article.

TL;DR

Have your users try cifs:// instead of smb:// (assuming your Windows share supports CIFS)...and hope that 10.9.4 comes with an SMB2 fix. :)