Particular query causes ADO Recordset to fail with E_FAIL - sql-server-2005

Question

i'm trying to run (two) queries against SQL Server 2005 using ADO:
SELECT
sp.nt_username AS NTUsername,
sp.hostname AS HostName
FROM sys.dm_tran_locks tl
INNER JOIN master.dbo.sysprocesses sp
ON tl.request_session_id = sp.spid
WHERE tl.resource_type = N'APPLICATION'
AND tl.resource_database_id = (
SELECT dbid
FROM master.dbo.sysprocesses
WHERE spid = ##spid)
and the SQL Server 2000 compatible version:
SELECT
sp.nt_username AS NTUsername,
sp.hostname AS HostName
FROM master.dbo.syslockinfo sli
INNER JOIN master.dbo.sysprocesses sp
ON sli.req_spid = sp.spid
WHERE rsc_type = 10 --10=Appliction
AND rsc_dbid = (
SELECT dbid
FROM master.dbo.sysprocesses
WHERE spid = ##spid)
The query executes fine:
IRecordset rs =new Recordset();
rs.CursorLocation = adUseClient; //the default for a Recordset is adUseServer (Connection.Execute's default is adUseClient)
rs.CursorType := adOpenForwardOnly; //the default
rs.Open(szQuery, conn.ConnectionObject,
adOpenForwardOnly, //CursorType
adLockReadOnly, //LockType
adCmdText);
But then checking the status of BOF or EOF:
if (rs.EOF) then
triggers an exception:
HRESULT: 0x80004005 (Unspecified error)
Error message: "Data provider or other service returned an E_FAIL status"
What is about this query that causes ADO to fail so miserably?
Note: There really is a matching row:
The provider i'm using in the connection string is Provider=SQLOLEDB.
Bonus Chatter:
sysprocesses
nt_username nchar(128)
hostname nchar(128)
and querying for both - but one at a time - works, e.g.:
SELECT
sp.nt_username AS NTUsername
and
SELECT
sp.hostname AS HostName
work. Querying for both fail.

Answer 1

i found the problem. It's a known issue with SQL Server 2005 and ADO:
Even though nt_username and hostname already are nchar(128), you need to manually cast them to nchar(128)
SELECT
CAST(sp.nt_username AS nchar(128)) AS NTUsername,
CAST(sp.hostname AS nchar(128)) AS HostName
FROM sys.dm_tran_locks tl
INNER JOIN master.dbo.sysprocesses sp
ON tl.request_session_id = sp.spid
WHERE tl.resource_type = N'APPLICATION'
AND tl.resource_database_id = (
SELECT dbid
FROM master.dbo.sysprocesses
WHERE spid = ##spid)
There is also a known bug with SQL Server 2005 and ADO and the use of ##spid in a query; you cannot do it. Fortunately i can, in this case, use DB_ID():
SELECT
CAST(sp.nt_username AS nchar(128)) AS NTUsername,
CAST(sp.hostname AS nchar(128)) AS HostName
FROM sys.dm_tran_locks tl
INNER JOIN master.dbo.sysprocesses sp
ON tl.request_session_id = sp.spid
WHERE tl.resource_type = N'APPLICATION'
AND tl.resource_database_id = DB_ID()
Bada-bing.
SQL Server 2005 bug.
It might still exist in SQL Server 2008, SQL Server 2008 R2, SQL Server 2012