Exception is :Format of the initialization string does not conform to specification starting at index 0.

What does it means???

<vb> 

   Private Sub cmdok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdok.Click

        If txtnew.Text = "" Or txtconform.Text = "" Or txtold.Text = "" Then
            MsgBox("Fill data into every field", MsgBoxStyle.Exclamation, "Null data Field")
        End If

        If txtnew.Text = txtconform.Text Then
            Try
                strsql = "UPDATE login SET Password= '" & txtnew.Text & "' WHERE Password = '" & txtold.Text & "' "
                cnsql = New OleDbConnection(strsql)
                cnsql.Open()

                cmsql = New OleDbCommand(strsql, cnsql)
                cnsql.Close()
                cmsql.Dispose()
                cnsql.Dispose()
            Catch ex As OleDbException
                MsgBox(ex.Message, MsgBoxStyle.Critical, "Oledb error")
            Catch exp As Exception
                MsgBox(exp.Message, MsgBoxStyle.Critical, "General")
            End Try

 </vb>

 That's probably because you tried to use the sql string as the connection string

Try
               strsql = "UPDATE login SET Password= '" & txtnew.Text & "' WHERE Password = '" & txtold.Text & "' "
                cnstr = "server=DBSERVER;User id=USER;password=PASSWORD;database=DB"
                cnsql = New OleDbConnection(cnstr)
                cnsql.Open()

                cmsql = New OleDbCommand(strsql, cnsql)
                cnsql.Close()
                cmsql.Dispose()
                cnsql.Dispose()
            Catch ex As OleDbException
                MsgBox(ex.Message, MsgBoxStyle.Critical, "Oledb error")
            Catch exp As Exception
                MsgBox(exp.Message, MsgBoxStyle.Critical, "General")
            End Try

A great resource for connection strings: http://www.connectionstrings.com/

befor closing connection use

cnsql.ExecuteNonQuery()

and try