On our SharePoint 2007 SP1 farm, when using web folders (WebDAV), certain files cannot be copied into a web folder (via WebDAV), but upload just fine when Internet Explorer's "Upload" capability is used.
Dragging one of these files into a web folder yields this error dialog: "Cannot copy <filename> - Invalid MS-DOS function".
This is definitely NOT a file naming problem (e.g., illegal characters like & and ?). The file names are ordinary, and if you rename the file, the problem stays.
We've seen this happen for XLS documents created by older versions of MS Office, for some PDFs, and for some JPEGs. So the type of the file is quite varied.
We did find a workaround for Excel files that have this problem: load them into Excel 2007 and just save them. The problem goes away for that file. SharePoint is clearly rejecting something in the CONTENT of the file.
As noted, the problem doesn't happen when you upload a file through the web UI. This is consistent with this explanation. That process ignores all the file's original attributes, like Author and Last Modified Time, so the problem doesn't occur.
I would call this "behavior" a bug, or at the very least, a poor design choice by Microsoft. Why not just ignore the extra attributes? The Web UI ignores them all!
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