If you get the error message, "Cannot open the file "*****.INDD". Adobe InDesign may not support the file format, a plug-in that supports the file format may be missing, or the file may be open in another application." when trying to open an Adobe file of the InDesign flavor, then there might be a solution:

See it here in this video. Basically, it comes down to the good, old fashioned "Type & Creator" being zapped, by emailing the file or via transfer from one computer to a server. (You should always compress and thus protect the document first through that compression.)

For more info, see the blog post on Markzware.com here:
http://www.markzware.com/blogs

We used the free Text Editor, 0xED for this task. I knew the file was really sick when nothing recognized it; thus more (actually less) than just corrupt.

If you have a bad or broken InDesign file, Markzware offers a no-cure, no-pay $99 service to try and fix them for you. Email: sales AT markzware.com for more details. (less info)