after update picture is erased

hello every one
i got a students database with name and picture
now when i add new stud and a pic everything is ok even when i change his pic
but when i edit the same stud an change is phonenumber or something and i press update
then the pic disappears from the database also.im using access
this is the code for the update
**********************

Cn.Execute "UPDATE Students SET " & _
"StudName= '" & RplS(Txt(0).Text) & "', " & _
"StudAddress= '" & RplS(Txt(1).Text) & "', " & _
"StudCelular= '" & RplS(Txt(2).Text) & "', " & _
"StudPhone= '" & RplS(Txt(3).Text) & "', " & _
"StudEmail= '" & RplS(Txt(4).Text) & "', " & _
"StudBirth= #" & MyDate(PickBirth.Value) & "#, " & _
"Photo= '" & CustPhoto & "' " & _
"WHERE StudID= " & FrmStudents.LsVw.SelectedItem.Tag
thnx for the help