There are active or pending disk writes, it won't let you alter the partition, yes doing it from a liveusb will work, can also try a reboot, and try again, if it is your / or /home then a liveusb will be the best
There are active or pending disk writes, it won't let you alter the partition, yes doing it from a liveusb will work, can also try a reboot, and try again, if it is your / or /home then a liveusb will be the best