excel writer

I generate the xls with excel writer, but when try to open with office 2007 the program show a message that said 'the file that try to open xxx.xls have other format that specified by the extension would yo u like to open it?'

what have to do to dissapear this message and open correctly the file?

thank you

after i updated to PHP 5.3

i become the same message and when i try to open it, Excel 2007 displays a Site with no formattings, beginning with the Error MSG!

Can someone help?

thanks

I've got the same error with 5.2.9 :-(