Hi,
looks like your tape pool
where your disks should migrate into
is either full or set readonly.

This would prevent reclamation as well - there
has to be writable 
either "empty" or "filling" media in the pool
for the reclamation to occur.
Alternatively the limit of scratch tapes
must be set accordingly high.

Check your tape pool settings as well, the storage pool
per se can be set readonly as wll, not only tapes.

If your tape pool were OK,
the overnight backups would not fail
but would use tapes instead of disk storage pool.

Another idea: 
Check whether the tape pool you speak about
is really set as "next pool" for your disk storage pool

regards
Juraj salak