Word cannot open this document. The document might be in use, the document might not be a valid Word document, or the file name might contain invalid characters (for example, \/).
for excel, the following error:
'JCIEUSA:filename.xls' could not be found. Check the spelling of the file name, and verify that the file location is correct.
JCIEUSA is the name of our NAS. I've seen the same problem but with a Synology NAS on other threads attributed to a bug with the NAS device, but since other files (pdfs etc) open just fine I think it must be a problem with Office.