Why Does The Index Lock My Updates In SQL Server 2005?

When one process has one record locked in Update-Mode then an other process can't update any other records on that table with some queries, other queries that access the same records (but with a different WHERE statement) will execute.
This problem occurs with SQL Server 2005, but it didn't with SQL Server 2000 (or any other database).

The problem:
-Process 1 locks a record in the table, and keeps it in Update-Mode, because the user is editing it. (Using OLEDB Pessimistic Cursor-locking)
-Process 2 wants to update an other record, buts gets a "Lock timeout" when using one query but not with another.

For example this query will work :
UPDATE gwseqnumber SET nextseqnr = 3 WHERE row_id = 110;

But this qeury will give me a "Lock timeout" :
UPDATE gwseqnumber SET nextseqnr = 3 WHERE name = 'REC_2';

But it is the same record!!
The record with name = 'REC_2' has the row_id = 110, both values are unique in the table.

The data:
The table [gwseqnumber] has the following CREATE statement:
CREATE TABLE GWSEQNUMBER
(
    NEXTSEQNR                      INTEGER,
    NAME                      CHAR (20),
    ADMINISTRATIONCODE             INTEGER,
    FINDHIGHESTNUMBER              CHAR (1),
    CLOSEDYN                       CHAR (1),
    ROW_ID                      INT IDENTITY(1,1) NOT NULL
);

CREATE INDEX KEY_1 ON GWSEQNUMBER (NEXTSEQNR);
CREATE UNIQUE KEY_2 ON GWSEQNUMBER (ADMINISTRATIONCODE, NAME, IDENTIFIER);
CREATE UNIQUE INDEX KEY_3 ON GWSEQNUMBER (ROW_ID);

Both KEY_2 and KEY_3 are unique, KEY_1 is not.


If I remove the index on the NEXTSEQNR column (the index named KEY_1) then both these queries will work, so it is obviously related to the index.
Altough the index is obsolete and can be removed from this table, it should not result in bogus locking errors.

Even when i removed the index not all the queries will work. (With work i mean not run into a locking error, while the record is not even locked.)



Solutions tried:
- Set the compaitiblity level of the databsae back to 80 (for SQL Server 2000 compatibility).
- I have already tried to disable Page-Locking on all the indexes of this table.


So why does the index lock my updates in SQL Server 2005?
And how do i fix it so my database does not run into these locks?