You'll need to be using the gfwl remover to follow these steps. If your save is DLC dependent 
you wont be able to load it with the gfwl remover, so you'll have to export your save at each 
step. That's added complication which I'm not going to go in to; you'll have to combine these 
instructions with the exporting savegames instructions yourself.

MAKE A COPY OF YOUR SAVE WITH THE BACKUP MANAGER BEFORE STARTING!!!

--- Steps to follow to fix a corrupted save ------

There's several different bugs in fable that can result in corrupted save, so the first thing 
you need to do is to discover your exact problem.

--- A zeroed save file ---------------------------

This is potentially the nastiest bug I've seen, because depending on which files it hits, you 
can lose progress. Occasionally, when writing out one or more save files, fable will fill it 
with zeros instead of writing out the actual save data. Even the checksum, which is appended 
later, is zeroed, so I have no clue how this happens. (Something that most of the other save 
bugs have in common, actually. :p)

To see if this is your problem, select the save in the save editor, and check the right hand 
text box. If it displays a warning about entityuid or saveuid looking broken, then this is your 
problem. If the save editor crashes, then this is probably still your problem, but you've got a 
considerably worse case of it. If it's only a *uid file, use the 'fix broken entityuid' or 'fix 
broken saveuid' options as appropriate.

If the editor can't even open your save, then you're going to have to do some work manually to 
get the save to a point the editor can open it. First locate another save made by the same xuid 
as the broken one. (If you don't have one, start a new game, and quicksave after choosing your 
outfit.) First copy the chaptersave file from the new save file on top of the broken one, and 
see if you can now open it in the editor. If you can't try overwriting leaderboardstatssave. If 
you still can't, then you're going to end up losing data. Delete herosave and mainsave, and 
replace them with the failquestherosave and failquestmainsave files. If you still can't open 
it, then your save is a complete loss. If you can, then check entityuid/saveuid as above.

--- Mismatched checksums -------------------------

Sometimes the gfwl encryption goes wrong, and the checksum recorded in the file will not be 
decryptable. This one's easy to fix; just use the recompute all checksums option, and load your 
save with the gfwl remover.

--- Incorrect xuid -------------------------------

Instead of relying purely on the gfwl encryption, fable 3 also makes an independent record of 
your remote xuid, and if this xuid doesn't match the xuid of a user trying to load the save, it 
will refuse to load the save. Alas, again for no real reason, fable will occasionally write the 
wrong xuid into the save file, with the result that no-one will be able to open it again.

This one is hard to diagnose if you're playing online, because it's not obvious what your 
remote xuid should be. Offline is far easier, whether using the gfwl remover or not: Since you 
don't have an remote xuid while offline, fable just uses your local xuid instead, so your 
remote and local xuids should be identical. Select your broken save, and check if the local and 
remote xuids are the same. If they aren't, click edit, and adjust the remote xuid fields 
appropriately. You can also select another save belonging to the same user, click 'mark for 
xuid transplant', select the broken save, and click 'perform xuid transplant'.

The default xuid for the gfwl remover is 1000100010001000, so to solve any xuid problems, put the save into a folder called 1000100010001000, and then edit the save and set both the upper and lower parts of the remote xuid to 10001000.

--- Corrupted hero -------------------------------

This one is pretty much impossible to diagnose. Sometimes the herosave will simply contain the 
wrong data, or have some little anomaly that fable doesn't like. If none of the above problems 
apply to you, then try using the 'revert to last quest' option, which will reset your progress 
back to the start of your last quest, but which will clear away any issues with the current 
version of your hero.