Differential backup always error

[john.g...@gmail.com]

Full and Imcremental backup have a volstatus of 'Full'

Seems the Differential backups are always in error, but cannot see why.

*list volumes
Pool: Differential
+---------+-------------------+-----------+---------+---------------+----------+--------------+---------+------+-----------+-----------+---------------------+---------+
| mediaid | volumename        | volstatus | enabled | volbytes      | volfiles | volretention | recycle | slot | inchanger | mediatype | lastwritten         | storage |
+---------+-------------------+-----------+---------+---------------+----------+--------------+---------+------+-----------+-----------+---------------------+---------+
|     198 | Differential-0192 | Error     |       1 |   113,542,541 |        0 |    2,592,000 |       1 |    0 |         0 | File      | 2020-10-20 14:23:13 | FILES   |
|     200 | Differential-0200 | Error     |       1 |   794,556,097 |        0 |    2,592,000 |       1 |    0 |         0 | File      | 2020-10-20 14:23:20 | MAIL    |
|     201 | Differential-0201 | Error     |       1 | 6,657,210,764 |        1 |    2,592,000 |       1 |    0 |         0 | File      | 2020-10-21 22:35:44 | FILES   |
|     202 | Differential-0202 | Error     |       1 | 1,615,609,091 |        0 |    2,592,000 |       1 |    0 |         0 | File      | 2020-10-21 23:01:08 | MAIL    |
|     207 | Differential-0207 | Error     |       1 | 3,024,361,212 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-22 22:38:18 | FILES   |
|     208 | Differential-0208 | Error     |       1 |   807,577,575 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-22 23:01:04 | MAIL    |
|     209 | Differential-0209 | Error     |       1 | 3,169,427,063 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-23 22:39:00 | FILES   |
|     210 | Differential-0210 | Error     |       1 |   816,277,450 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-23 23:00:56 | MAIL    |
|     211 | Differential-0211 | Error     |       1 |         2,281 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-24 21:00:16 | File    |
|     219 | Differential-0219 | Error     |       1 |   308,996,372 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-25 22:33:03 | FILES   |
|     220 | Differential-0220 | Append    |       1 |   801,636,806 |        0 |    1,900,800 |       1 |    0 |         0 | File      | 2020-10-25 23:01:06 | MAIL    |
+---------+-------------------+-----------+---------+---------------+----------+--------------+---------+------+-----------+-----------+---------------------+---------+


As you can see - all the Differential volumes have a status of 'Error'.

Why is this?

What can I look at to see the 'error'?