cannot open xml file in excel 2007 as a read-only workbook

i drap a large xml file into excel 2007. choose "As a read-only workbook" mode.

then i get "This XML file cannot be opened because of an error. Check to make sure the file is a valid XML file, and that the XML syntax is correct. You can also try re-creating the file and closing other application before you attempt to open it again"

it does not say any specific syntax or tag error.

how can i find the error or any way i can correct the file.

thanks in advance