can't open the powerpoint 2003 files using powerpoint 2003. file convertor for office 2007 was already installed. error 'powerpoint can't open the type of file represented by .. C:\xxxx\eee\.ppt'

when use powerpoint viewer 2003 to open, it gives 'powerpoint viewer cannot open the file 'eee.ppt' because the file is not a powerpoint file.

when use powerpoint viewer 2007 to open, it also gives the same error as using powerpoint viewer 2003