Hi, i prepared an excel sheet using cakePHP frame work with 'application/vnd.ms-excel' mime type.when i am trying to open it in excel 2013 it prompt like

The file format and extension of 'filename.xls' don't match. The file could be corrupted 
 or unsafe.Unless you trust it source,don't open it Do you want to open it any way ?

Please help me how to solve this issue

Hi

According to your description, you may follow these steps to fix it

1. Go to HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Excel\Security

2. Edit --> New --> DWord value

3. Name it ExtensionHardening. It will be on 0 by default.0

The file has to have an XLS extension, the key won't work for XLSX and the file wouldn't open using it.

    Key: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security
    Value: (DWORD)"ExtensionHardening" = [0 = Disable check; 1 = Enable check and prompt; 2 = Enable check, no prompt deny open]
    Default setting if value not present is 1 (enable and prompt).

Hope it helps