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Hi JB Brownasdasd,

Thank you for visiting our forum.

The forum that you posted is the English only forum for Microsoft Office. To avoid any misunderstanding that may be caused by the translation tool and better help you, please describe your issue in English. Alternatively, you could post this issue in other forums with the right language.

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Regards,

Emi Zhang
TechNet Community Su

Hi,

I can translate it.I use the 2013 Excel

The problem is the following. Whenever I create the xlsx document with RIGHT CLICK - CREATE - NEW EXCEL DOCUMENT, it does not open and shows the error: Can not open the file because the format or file extension are not valid. Make sure that the file is not damaged and the extension of its name corresponds to its format.

If i firstly enter the excel program, and save the document with File - Save as, this error doesnt occur.

Can you please help what may contain a problem

Thank you very much

Hi JB Brownasdasd,

Based on your error message, this problem has been confirmed to be caused by malware on the affected machine. There are now two known variants of malware which causes this problem: Win32/Crilock.A and Win32/Buma!rts. They have both been identified as a new family of ransomware.

I suggest you read this Blog about your issue:
http://blogs.technet.com/b/the_microsoft_excel_support_team_blog/archive/2013/09/07/quot-cannot-open-the-file-because-the-file-format-or-extension-is-invalid-quot-opening-office-files.aspx

Hope it's helpful.

Regards,

Emi Zhang
TechNet Community Su