At the setting for CF card at the item No.19 to select "use" or "not use", the key indicator can not be changed from "off" to "on".
Do you use a CF card which Kyoritsu did not check and confirmed the operation?
Please refer to here for the CF cards which Kyoritsu checked the operation with Model 6300.
Are you formatting the CF card via computers?
It is possible that a CF card which was formatted via a personal computer cannot be used with model 6300. Please format the CF card which was formatted via a personal computer or the brand new CF card as per the procedure described in Setting 20 (Formatting of CF card).
*When the CF is formatted, all the data recorded in the CF card will be deleted.