Error saving files to MWB1TB

Ever since I installed new laptops in my small office with Win7 installed I get the following error when overwriting files on the WD share: 

A file permission error occurred. Failed to connect to network.

The file then disappears off the share. This does not happen all the time though.

This happens when I save a file that that was modified and I have received it back in Outlook. I try save it over the existing file.