If you cannot see the fpdatasources folder in SharePoint Designer 2007 and are sure you have Site Collection/Owner permissions then perform this step …
Go to “Data View” on the SharePoint Designer 2007 menu and then click on “Manage Data Sources”
Now expand “_catalogs” in SharePoint Designer 2007 and you should see fpdatasources.
I needed to change the permissions on this folder so that everyone had read access (as a standard contribute level user could not access the site without elevating their permissions to approver level). If you are unsure how to change permissions on fpdatasources then right click on it and select “Properties”.
Then click on the “Security” tab then click on the link “Manage permissions using the browser”. Add the relevant groups that require read access and then save.