Nikon D7200 body - Manual (Page 33)

33 Menu Guide
D
Folder and File Numbers
If the current folder is numbered 999 and contains 999 pictures or a
picture numbered 9999, the shutter-release will be disabled and no
further photographs can be taken. To continue shooting, create a
folder with a number less than 999, or select an existing folder with a
number less than 999 and less than 999 images.
A
Startup Time
Additional time may be required for camera startup if the memory card
contains a very large number of files or folders.