unfinished process in MS SQL 2005

I'v got a problem with an SAP B1 with MS SQL 2005.

In application log, there's an entry:

3   06.07.2015 23:59:10 ITKService  Previous transaction has not been finished, delaying current transaction.

When I look for open transaction (DBCC OPENTRAN), I cannot find it one:

No active open transactions.
DBCC execution completed. If DBCC printed error messages, contact your system administrator.

In activity monitor there's one entry (same user, that runs application B1), that's got an entry with open transaction...

I killed that session several times and also restarted server. No success. Any ideas?

Best regards Patrick