Ok. I wanted to isolate that it is not an upload issue. I was thinking that the computer uploading the doc files could be corrupting the file. But this is something rare that it does so only for .doc files.
I have 3 requests to ensure it is not an extention problem:
1. Can you rename an .xls file to .doc and then upload .. then when downloaded to Computer A have it renamed back to .xls and see if it can open it. (you may have to enable "show known file extensions")
2. Reverse "1" by renaming a good .doc to .xls ... then back to .doc after downloading.
3. If you zip the .doc file and upload it, please check if you can open it at Computer A after downloading and unzipping the file.