Try this

Public Function Bin_conv(Byval value as long) as string

Dim multi As Long
Dim binary As Variant

multi = 0
binary = 0

If value > 2048 Then
msgbox = "**Overflow**"
Exit Function
End If
Do While (value > 0)
remainder = value Mod 2
value = Fix(value / 2)
If remainder = 1 Then binary = binary + 10 ^ multi
multi = multi + 1
Loop
Bin_conv = binary
End Function