excel cannot open the file filename.xlsx because the file format or file extension is not valid.

%3CLINGO-SUB%20id%3D%22lingo-sub-3209613%22%20slang%3D%22en-US%22%3Eexcel%20cannot%20open%20the%20file%20filename.xlsx%20because%20the%20file%20format%20or%20file%20extension%20is%20not%20valid.%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-3209613%22%20slang%3D%22en-US%22%3E%3CP%3EI've%20tried%20the%20basic%20repair%2Fextract%20answers%20given%20in%20the%20numerous%20different%20forums%20but%20nothing%20will%20work.%20Please%20help%2C%20very%20important%20school%20project%20with%2010%2B%20hrs%20of%20work%20into.%26nbsp%3B%3C%2FP%3E%3C%2FLINGO-BODY%3E%3CLINGO-LABS%20id%3D%22lingo-labs-3209613%22%20slang%3D%22en-US%22%3E%3CLINGO-LABEL%3EExcel%20for%20web%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EFormulas%20and%20Functions%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EOffice%20365%3C%2FLINGO-LABEL%3E%3C%2FLINGO-LABS%3E%3CLINGO-SUB%20id%3D%22lingo-sub-3213147%22%20slang%3D%22en-US%22%3ERe%3A%20excel%20cannot%20open%20the%20file%20filename.xlsx%20because%20the%20file%20format%20or%20file%20extension%20is%20not%20valid.%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-3213147%22%20slang%3D%22en-US%22%3EIf%20you%20open%20the%20file%20in%20Notepad%2C%20what%20does%20it%20show%3F%3C%2FLINGO-BODY%3E
Occasional Visitor

I've tried the basic repair/extract answers given in the numerous different forums but nothing will work. Please help, very important school project with 10+ hrs of work into. 

2 Replies
If you open the file in Notepad, what does it show?
Is the full path of file too long? Sometimes windows cannot open Excel file if path is too long. Try keeping the file on some shorter path (like desktop)