NHibernate MismatchedTreeNodeException

Question

I have a DB handling app in which I came across a problem while updating many to many relation's objects. I have a table Devices and a table Admittances that are connected with one another with a third table Admittances_Devices. Every device can be admitted many times and every admittance can have multiple devices. I put my mappings and classes below

public class Device
    {
        public Device()
        {
            Admittances = new List<Admittance>();
        }
        public virtual int ID { get; set; }
        public virtual string SerialNumber { get; set; }
        public virtual Manufacturer Manufacturer { get; set; }
        public virtual Model Model { get; set; }
        public virtual Volume Volume { get; set; }
        public virtual Type Type { get; set; }
        public virtual string Distinguishing { get; set; }
        public virtual IList<Admittance> Admittances { get; set; }
    }

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="MeraserwHub.DBClasses" assembly="MeraserwHub">
    <class name="Device" table="Devices">
        <id name="ID" column="DeviceID" >
            <generator class="identity" />
        </id>
        <property name="SerialNumber" column="SerialNumber" />
        <property name="Distinguishing" column="Distinguishing" />
    
        <many-to-one name="Manufacturer" lazy="proxy" unique="true" column="Manufacturer" not-found="ignore" cascade="all-delete-orphan"/>
        <many-to-one name="Model" lazy="proxy" unique="true" column="Model" not-found="ignore" cascade="all-delete-orphan"/>
        <many-to-one name="Volume" lazy="proxy" unique="true" column="Volume" not-found="ignore" cascade="all-delete-orphan"/>
        <many-to-one name="Type" lazy="proxy" unique="true" column="Type" not-found="ignore" cascade="all-delete-orphan"/>

        <bag name="Admittances" table="Admittances_Devices" inverse ="true" lazy="true" cascade="save-update">
            <key column="DeviceID"/>
            <many-to-many class="Admittance" column="AdmittanceID"/>
        </bag>
    </class>
</hibernate-mapping>

public class Admittance
    {
        public Admittance()
        {
            Devices = new List<Device>();
        }
        public virtual int ID { get; set; }
        public virtual string Number { get; set; }
        public virtual Client Client { get; set; }
        public virtual User User { get; set; }
        public virtual DateTime Date { get; set; }
        public virtual string Notes { get; set; }
        public virtual IList<Device> Devices { get; set; }
    }

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="MeraserwHub.DBClasses" assembly="MeraserwHub">
    <class name="Admittance" table="Admittances">
        <id name="ID" column="AdmittanceID" >
            <generator class="native" />
        </id>
        
        <property name="Number" column="Number" />
        <property name="Date" column="Date" />
        <property name="Notes" column="Notes" />
        
        <many-to-one name="User" lazy="proxy" column="[User]" />
        <many-to-one name="Client" lazy="proxy" column="Client" />

        <bag name="Devices" table="Admittances_Devices" cascade="save-update" generic="true">
            <key column="AdmittanceID"/>
            <many-to-many class="Device" column="DeviceID"/>
        </bag>
    </class>
</hibernate-mapping>

When I want to update a device and admittance so I could add a record to each table I get an error. You can find the code of the methods and the error below.

Device device = menu.allDevicesList[cbx_serialNum.SelectedIndex];

device.Admittances.Add(toAddAdmittance); `toAddAdmittance is an object defined earlier`
toAddAdmittance.Devices.Add(device); 
dbConnection.UpdateDevice(device); `dbConnection is NHibernate class object`
dbConnection.UpdateAdmittance(toAddAdmittance);

   public void UpdateDevice(Device device) `the method for admittances looks exactly the same`
        {
            try
            {
                using (mySession.BeginTransaction())
                {
                    mySession.Query<Device>()
                      .Where(a => a.ID == device.ID)
                      .UpdateBuilder()
                      .Set(a => a.SerialNumber, device.SerialNumber)
                      .Set(a => a.Manufacturer, device.Manufacturer)
                      .Set(a => a.Model, device.Model)
                      .Set(a => a.Volume, device.Volume)
                      .Set(a => a.Type, device.Type)
                      .Set(a => a.Distinguishing, device.Distinguishing)
                      .Set(a => a.Admittances, device.Admittances)
                      .Update();

                    mySession.Transaction.Commit();
                }
                //MessageBox.Show("Dane urządzenia zostały zaktualizowane");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

Error has an inner exception "MismatchedTreeNodeException(140!=3)" and the stack trace as below. For admittances I get the same error.

w NHibernate.Hql.Ast.ANTLR.ErrorCounter.ThrowQueryException()
w NHibernate.ql.AsStŁ.ANT LR.Exec.BasicExecutor..ctor(lStatement
statement, IQueryable persister)
w
NHibernate.Hql.Ast.ANTLR.QueryTranslatorlmpl.BuildAppropriatestatem
entExecutor(lStatement statement)
w
NHibernate.Hql.Ast.ANTLR.QueryTranslatorlmpl.DoCompile(lDictionary2
replacements, Boolean shallow, 5tring collectionRolej
w
NHibernate.Hql.AsŁANTLR.ASTQueryTranslatorFactory.CreateQueryTransl
ators(IQueryExpression queryExpression, IASTNode ast, String
queryldentifier, String collectionRole, Boolean shallow, IDictionary2
filters, ISessionFactorylmplementorfactory]
w
NHibernate.Hql.Ast.ANTLR.ASTQueryTranslatorFactory.CreateQueryTransl
ators(IQueryExpression queryExpression, String collectionRole, Boolean
shallow, IDictionary2 filters, ISessionFactorylmplementorfactory]
w
NHibernate.Engine.Query,.QueryPlanCache.GetHOQLQueryPlan(IQueryExpr
ession queryExpression, Boolean shallow, IDictionary2 enabledFilters)
w
NHibernate.lmpl.Abstractsessionimpl.GetHOQLQuerPlan(IQueryBD<pressio
n queryExpression, Eeoolean shallow)
w NHibernate.lmpl.Abstractsessionimpl.CreateQuery(IQueryExpression
queryExpression)
w NHibernate.Linq.DefaultQueryProvider.ExecuteDml[T](QueryMode
queryMode, Expression expression]
w MeraserwHub.NHibernate.UpdateDevice(Device device) w
Ev Kodowanie CHepostMeraserwHubiMeraserwHubiyMeraserwHubiNH
ibernate.cs:wiersz 394

Please help guys, cause I've been struggling with this for some time already!