error : The multi-part identifier couldnt be bound.

Declare   @FromDatetime= '2011-02-12 00:00:00',

            @ToDatetime=  '2011-04-28 22:30:20';

Select enroll,Dim.regdate, Cls.ID,rn=ROW_NUMBER() over(partitiOnby enrollorderby Dim.regdate)

INTO #Qry From QR2 As Dim

WhereCast(Dim.regdateAsdatetime)between @From And @to

           And enroll not in(12345129,124818243)

           And Dim.Stud_ID notIN 112409,12349,12139,121349,213140,12134)

Createclusteredindex R_QOn #Qry(ID)

Select enroll,regdate INTO #Q_2 From #Qry Dim

     crossapply(Select distinct Cls.ID From Std_title cp

            Join Clsannels ClsOn cp.ref=Cls.ID

           And cp.Prof_ID=Dim.Stud_IDAnd Cls.classrm=1

         And Cls.Classtype=0And Cls.fk_org=500

       ) Cls                         

Select*INTO #temp From (    Select q1.rnAs rn1q2.rnAs rn2, q1.enroll,q1.IDAs c1, q2.IDAs c2   From #Q_2 q1 innerhash   Join #Q_2 q2 On q1.enroll=q2.enroll    And q2.rn=q1.rn+1And q1.ID<>q2.ID

                                   )tmry

DropTable #Qry

DropTable #temp

Error:

Msg 4104, Level 16, State 1, Line 14

The multi-part identifier "Cls.ID" could not be bound

Please help me to resolve this error? Any further advice to reduce the execution time would also be appreciated.

Thanks in advance for your support and help.

Thank You , Shan Ali Khan