PEAR Spreadsheet_excel_writer problem

Hi I have a class the utilizes the excel writer package but I'm having a few problems with it on my production server. My development server is a Windows XP Pro box running PHP version 4.3.5. On this box I dont get any problems and my class generates a valid excel document. My production server is a FreeBSD box running PHP version 4.3.4. With this box my class will create a excel document but when I go to open the file up, it comes back and tells me the file is unreadable as it is 0 bytes in size. I know the sql query I'm running is returning data as I can create a tabbed delimited excel document from it. Can anyone help me with this or point me in the right direction, as its driving me mad. Thanks Alex