I'm using the backup utilities with plesk, I see the following in the log:

Found unreferenced record for domains id = 15 in 'stat' database table.
Found unreferenced record for domains id = 15 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.
Found unreferenced record for domains id = 16 in 'stat' database table.

Is this bad? What does it mean?

Looks like a domain's statistics still exist in the Plesk database but the domain's record itself no longer exists. Install phpmyadmin and check out the 'stat' table in the 'psa database. Search for any records with a 'dom_id' of 15 or 16, you can then safely delete any records found.

Cool just the hint I needed!

I see:

mysql> select * from stat where dom_id=15;
+--------+------------+----------+
| dom_id | date | transfer |
+--------+------------+----------+
| 15 | 2002-10-04 | 0 |
| 15 | 2002-10-05 | 0 |
+--------+------------+----------+
2 rows in set (0.00 sec)
mysql> select * from stat where dom_id=16;
+--------+------------+----------+
| dom_id | date | transfer |
+--------+------------+----------+
| 16 | 2002-09-18 | 0 |
| 16 | 2002-09-19 | 0 |
| 16 | 2002-09-20 | 0 |
| 16 | 2002-09-21 | 0 |
| 16 | 2002-09-22 | 0 |
| 16 | 2002-09-23 | 0 |
| 16 | 2002-09-24 | 0 |
| 16 | 2002-09-25 | 0 |
| 16 | 2002-09-26 | 0 |
| 16 | 2002-09-27 | 0 |
| 16 | 2002-09-28 | 0 |
| 16 | 2002-09-29 | 0 |
| 16 | 2002-09-30 | 0 |
| 16 | 2002-10-01 | 0 |
| 16 | 2002-10-02 | 0 |
| 16 | 2002-10-03 | 0 |
| 16 | 2002-10-04 | 0 |
+--------+------------+----------+
17 rows in set (0.00 sec)

Your right there is no info in there

mysql> delete from stat where dom_id=15;
Query OK, 2 rows affected (0.00 sec)
mysql> delete from stat where dom_id=16;
Query OK, 17 rows affected (0.00 sec)

did the trick!

Good to hear