It's a long time since I used a 1D Mark II - but I seem to remember that the useable CF capacity was limited to 2Gb (related to the old MSDOS / Windows file structures used]. Not a problem at the time since since 2GB cards were the max in normal use. An unsupported fix was, however, to format the CF card on a modern PC that supported larger capacities. Even so I would not have tried anything larger than 4Gb in those days. I think it was the Mark IIN that allowed for formatting larger capacity cards. Try re-formating a CF card on a more recent model 1D (IIN or later) or on a newish PC and then shooting until the camera thinks it has run out of space.