The error only occurs when transferring some WA files via ftp using the Files panel in DW. Don't know why this one 'ProductsDb.php' file is in the middle of several error messages.
Deleted all the existing 'ProductsDb.php' files and created new - same errors.
FTP access is in PM.
Drag the checkout.php page to the server in DW and check 'include dependent files'. The Details list will show the error and a gray box with an x in it will appear next to the Connections folder.