eperdos

I have a sony mz-nh700 for 1 and a half year.I always use the 1gb disc provided.never had problems when recording.a few days ago I used the md as a portable device and stored on it some files from the internet.after that(anyway I`m not sure if this is the cause) I can`t record, renam, delete on th disc.recording gos well until data writing, when I get the rec error message.same for all other writing actions. please someone give me a help here!!! maybe I deleted some of the files from the disc, but I have no clue how to discover this. I wait for some hElp!!!PLEASE!!!