[RESOLVED] Compile Error: Constant expression required? Help!

[Gamemaster1494]

It highlights this sub:

Public Sub CalculateBD(txtInput As TextBox, lblOutput As Label, lengthfornumber As Long)
    Dim i
    Dim character(Len(txtInput.Text))
    For i = 1 To Len(txtInput.Text)
        character(i) = Mid$(txtInput.Text, i, 1)
        If character(i) = "0" Or character(i) = "1" Then
        
        Else
            Call MsgBox("The data you entered is not a 1 or a 0! ", vbCritical Or vbDefaultButton1, "Incorrect Data!")
            Exit Sub
        End If
    Next i
    Dim multiplynumber As Long
    multiplynumber = 1
    For i = lengthfornumber To 1 Step -1
        If i = lengthfornumber Then
            multiplynumber = 1
        Else
            multiplynumber = multiplynumber * 2
        End If
        If character(i) = "1" Then
            lblOutput.Caption = lblOutput.Caption + multiplynumber
        End If
    Next i
End Sub

What it highlights is in bold. Please help. i do not understand why it is doing this...