Cannot change hosting type for a Plesk domain: Unable to load object of type SysUser with id

Connect to the server via SSH/RDP.

Backup Plesk database.

Run Plesk repair utility (for Windows, run Command Prompt first):

# plesk repair db

Confirm fix for all errors that begin with:

Inconsistency in the table 'web_users'
Inconsistency in the table 'smb_users'

Create the domain or set the necessary hosting type for the domain in the Plesk interface.

Connect to the server via SSH/RDP.

Backup Plesk database.

Enter Plesk database (for Windows, run Command Prompt first):

# plesk db

Make sure that there is no system user with ID from error message in Plesk database:

mysql> select * from sys_users where id=1;
Empty set (0.00 sec)

Find domain ID and make sure that hosting type for the domain is set to none :

mysql> select id, name, htype from domains where name like '%example.com%';
+----+-------------+-------+
| id | name | htype |
+----+-------------+-------+
| 76 | example.com | none |
+----+-------------+-------+
1 row in set (0.00 sec)

Find the inconsistent record in the hosting table:

mysql> select dom_id, sys_user_id, www_root from hosting where sys_user_id=1;
+--------+-------------+--------------------------------------+
| dom_id | sys_user_id | www_root |
+--------+-------------+--------------------------------------+
| 2 | 1 | /var/www/vhosts/example.com/httpdocs |
+--------+-------------+--------------------------------------+
1 row in set (0.00 sec)

Remove the inconsistent record using dom_id from previous step:

mysql> delete from hosting where dom_id=2;

Create the domain or set the necessary hosting type for the domain in the Plesk interface.