The error means, that this subquery:
SELECT T.USER_ID
FROM USER_OTHER_PRIVILEGES T
JOIN USERS U
ON U.ID = T.USER_ID
WHERE T.UOPM_ID = 17
AND T.PRIV_ID IN (719)
returns more that one row.
Please run this query and you will see that at least 2 user ids will appear.
The INSERT statements with the VALUE clause can insert only one row into the table, and it expects only one value for each column in the VALUES clause:
INSERT INTO table( col1, col2, col3 ) VALUES ( val1, val2, val3 )
You can't enter many values to one column in the row.
For example if this subquery returns three numbers: 1,2,3, you cannot insert one row in such a way:
+------+---------+---------+---------+-------+-----------+
| ID | PRIV_ID | UOPM_ID | USER_ID | ML_ID | PARENT_ID |
+------+---------+---------+---------+-------+-----------+
| 456 | 1792 | 17 | 1,2,3 | NULL | 1 |
+------+---------+---------+---------+-------+-----------+
I guess that you don't want to insert only one row, but you are going to insert one separate row for each entry returned by the suquery, like this:
+------+---------+---------+---------+-------+-----------+
| ID | PRIV_ID | UOPM_ID | USER_ID | ML_ID | PARENT_ID |
+------+---------+---------+---------+-------+-----------+
| 456 | 1792 | 17 | 1 | NULL | 1 |
+------+---------+---------+---------+-------+-----------+
| 457 | 1792 | 17 | 2 | NULL | 1 |
+------+---------+---------+---------+-------+-----------+
| 458 | 1792 | 17 | 3 | NULL | 1 |
+------+---------+---------+---------+-------+-----------+
In this case you can't use INSERT INTO ... VALUES ...
syntax,
you need INSERT INTO .... subquery
variant instead,
see this answer for more details: How can I insert values into a table, using a subquery with more than one result?
Your insert statement for such a case can be:
INSERT INTO USER_OTHER_PRIVILEGES (
ID, PRIV_ID,UOPM_ID,USER_ID,ML_ID,PARENT_ID
)
SELECT
PRIV_USER_OTH_ID_SEQ.NEXTVAL,
1792,
17,
T.USER_ID,
NULL,
1
FROM USER_OTHER_PRIVILEGES T
JOIN USERS U
ON U.ID = T.USER_ID
WHERE T.UOPM_ID = 17
AND T.PRIV_ID IN (719)