beejaydadeejay, I replied to the email you sent me but I got a Delivery Status Message of delay soon after so I don't know if you've received it yet.
Anyway, that email has nothing of help but I've since thought of a possible reason. Now, you appear not to know a lot about max drives but after transferring the option file onto the xbox maxdrive...it doesn't allow direct transfer to the xbox hard drive. For each file stored on the max drive there are usually 2 options: 'Copy' & 'Delete'. With the PES5 option file, the only option that appears is 'Delete'. So, the only way of getting the option file onto your xbox hard drive is to load up PES5, go to Options, PES Data, Copy Saved Data...go to 'Change' (changes from searching the hard drive for a file to the max drive), select the PES5 OF that is present on the max drive, and then you can save it onto your hard drive and therefore be able to use it. Now, a lot of the above might not make sense to you - but the point is that PES5 option files seemingly need to be transferred a different way to other game saves. So I don't know if you can use FTP whilst PES5 is loaded...I don't know enough about FTP...
When you say it works for you with other files, do you mean other PES5 option files or other games? Because most games can be 'copied' onto the hard drive directly using the max drive. If you have managed to put other PES5 OF's onto your hard drive using FTP, then I really don't know what the solution is - that's just the only thing I can think of.
All I can say is using a max drive is the only sure-fire way of getting it to work.