Savegame corruption.

[Daemos Avetorii]

I just had to delete several days worth of a character savegame because while the savegame would still load, it would not allow me to save a new one. Before I deleted the savegame, I tested what would happen if I made a new character and save right in the prison. It saved there without crashing. Not sure exactly why the other one won't save, not even a new one. Any clues to what can be done to prevent this from happening again? The only anomaly I can report is that the last 5 minutes before the crash, the game got very laggy. It never does, and my PC could handle 3-5 instances of Oblivion at the same time with no problem whatsoever. So I am not sure if there is a connection between the sudden lag and the savegame corruption/crash.

[Tingz0r]

The top Google search result suggests you need to change your character's name using the console.

player.setactorfullname "(name)"

Otherwise, I'd suspect any recent change in active mods could have broken it.