Getting and error msg "The file you are trying to open "xxx.xls"

Hi folks,

getting and error msg "The file you are trying to open "xxxxx.xls" is in a differernt format than specified by the file extension. Verify that the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now".

When I do, all the data, and formulas, everything looks like some sort of source code.

I am getting this for some files, and others open just fine.

I've tried the Open and Repair.
Used Free File Opener.
Tried different options with the Excel Options tab

the only thing that is different is that these files were restored from my backup and the ones that I can open, were not restored.

so much for the darn backup..

Would appreciate any suggestions.

jjjslj