When clickling a link within a wikipage to an attached DOC file in Confluence 5.7.1 a preview window (dark screen) opens. There it says "We can't preview this file. You'll have to download the file to view it.":

The same DOC file can be successfully viewed from the attachments list.

In addition our users are complaining about this error message because it does not support the user in finding the download link (in fact a very small icon in the upper right corner).