mount: /dev/ad1s1e: Operation not permitted

[Fira]

Hi list,

I want to mount my /dev/ad1s1e, but it produce error output :
root# mount /dev/ad1s1e /data1/
mount: /dev/ad1s1e: Operation not permitted

I've checked my /var/log/messages, but it doesn't show any message related
to that.
I've fsck that slice, and retried to remount, but it failed again.
Then, I add in my fstab this entry :
..snip..
/dev/ad1s1e             /data1 ufs    rw              2       2

and reboot my machine, but still the system didn't want to mount it.

This is my bsdlabel output :
root# /dev/ad1s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 488392002        0    unused        0     0         # "raw" part, don't
edit
  d: 163840000        0    4.2BSD     2048 16384 28552
  e: 122880000 163840000    4.2BSD     2048 16384 28552
  f: 163840000 286720000    4.2BSD     2048 16384 28552
  g: 37832002 450560000    4.2BSD     2048 16384 28552

In my understanding, ad1s1e has been formatted into ufs, and I think there
should be no problem to mount it.

So, where is the point of my mistake?

Thanks a lot for your responses.