cant run update sql due to lock violations

Hi Experts,
I'm trying to update a SQL table thru Access and getting the attached error, "cant update..due to lock violations", however there should be currently no users on the system, any idea whats causing it?
below is the SQL

UPDATE dbo_EmployeesUnitstbl INNER JOIN (SELECT dbo_EmployeesUnitstbl.EmployeesID
FROM dbo_Employeestbl INNER JOIN dbo_EmployeesUnitstbl ON dbo_Employeestbl.ID = dbo_EmployeesUnitstbl.EmployeesID
WHERE (((dbo_Employeestbl.Title)="rn") AND ((dbo_EmployeesUnitstbl.Unit) In ("MRDD","ddso","group home"))))
 AS a ON dbo_EmployeesUnitstbl.EmployeesID = a.EmployeesID SET dbo_EmployeesUnitstbl.Unit = "RN – GROUP HOME"
WHERE (((dbo_EmployeesUnitstbl.Unit)="RN - LTC"));

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