The file format and extension of 'report.xls' don't match. The file could be corrupt or unsafe.

[hmkhafan]

hi i'm create an excel with this class, but when i open file in excel this warning showing in open dialog:
"The file format and extension of 'report.xls' don't match. The file could be corrupt or unsafe."
is there a way for preventing this warning?

[Nolana30]

I have the same problem with opening the Excel file.
Is there solution for it?

[christophbee]

Is there already a solution for it? I am faced with the same issue now.

[ideiasfrescas]

Doesn't the docs state that this class supports only xlsx format?