Formula sqrt to VBA conversion

Hi Guys

In attached sample file I am trying to get F26 calculation...
The code does not error but the answer is an error...Any ideas

Option Explicit

Sub Test()
Dim CatSz As Long, Size As Long, Prop As Double, StdErr As Double
Size = [F23]
CatSz = [F24]
Prop = CatSz / Size
StdErr = Sqr((Prop * (1 - Prop) / Size))
End Sub