Excel files all open as corrupted files

[LeeM7879]

Hi.

I have a large amount of excel files stored in my dropbox.....

Yesterday they opened and worked ok, but today, they all generate an error when being opened which reads.....

"Excel cannot open the file '<filename>.xlsm' or <filename>.xlsx because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file"

This occurs on 4 different computers running the latest Office365 version.

Ive also tried downloading the file and then opening, but the same error message is generated.

The files also will not open in the online version of excel or the quickviewer.

We're talking about hundreds of excel files which were all working then suddenly are not.

Any help, or suggestions would be greatly appreciated.

Kind Regards

[Mark]

Have you tried restoring to yesterday's versions? https://help.dropbox.com/delete-restore/recover-older-versions

What about opening Excels from another Dropbox account or that is say emailed in to a person instead?

[LeeM7879]

In most cases, there are no restore options, as the files in question havent been opened for some time. I was able to restore a very limited amount of the files, but only the ones that were being worked on yesterday. So, in most cases, these files have been untouched but are now coming up as corrupt.

All new files that are created work ok and although i do not have access to another dropbox account, i can open excel files from other authors emailed to me.

Thank you for the response

[Mark]

So, Dropbox cannot alter files - if they are appearing corrupt they were uploaded corrupt. One thing to check is that they are local versions and not online-only files, which can cause issues. To test that do they work if you open via the website or not? 

Also think of things like updates that have happened to Excel could that have updated anything?

[LeeM7879]

I understand what youre saying, which is why Im at a complete loss as to how files that were working perfectly more than a month ago, which have not been opened can all suddenly become corrupted.

The files do not open from the web, or if they are downloaded first to make them local files.

I gave some consideration that it could be an excel update, but when the same behaviour occurs on 4 different machine it becomes very perplexing.