Try to open the file in Excel. Does this work? If not, it looks like the file is corrupted. Restore it from your backup. Create a new backup for the otehr files you process with your Matlab script. Afterwards start to examine your code: It is unlikely that Matlab xlsread damages files. On one hand it opens the file for reading only, on the other hand it has been tested and used millions of times. Perhaps the hard drive is corrupted (check this), or you have an fopen anywhere in your code. Maybe another user has written to the file, or it is a malware attack?
I did not write or do anything to the file?
Obviously you or somebody else did.
