X158: Cannot obtain or delete table locks in isolation level 5 or 6.

When working at isolation level 5 (dirty read) or level 6 (snapshot read), a transaction cannot acquire or drop table locks. Levels 5 and 6 are intended for read only. You cannot insert, update, delete, or alter database objects at these levels. Tables are accessible by other users.
Restriction: This topic applies to Windows environments only.