Can't remove folder: I/O error

Hello to all. I have instaled a my own firmware on mikrotik rbm450gx4 router.

I want to delete the folder nbproject but I get I/O error:

root@OpenWrt:/srv/www# rm -rf nbproject/
rm: can't remove 'nbproject/private': I/O error

This folder was included in my custom firmware.

Any idea what happens?