Error when resizing a ext4 partition
I encountered this same error because the partition was not mounted.
After creating a mount point and then mounting, resize2fs completed without error.
mkdir /temp-mount-point
mount /dev/sdb5 /temp-mount-point
resize2fs /dev/sdb5
resize2fs 1.42.13 (17-May-2015)
Filesystem at /dev/sdb5 is mounted on /temp-mount-point; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 699
The filesystem on /dev/sdb5 is now 1463818240 (4k) blocks long.