Userform textbox value based on combobox selection

Hi
have a userform2.
There is combobox7 and next to it is textbox4.
In sheet named sheet5, in range G5:G600 there are names and H5:H600 their staff numbers.
I am trying to get staff number in textbox4 based on what I select in combobox.
I am getting an error on following code.

Private Sub Combobox7_Change()

var1 = WorksheetFunction.VLookup(ComboBox7.Value, Worksheets("sheet5").Range("H5:H600"), 2, False)

txtweight.Value = var1


End Sub

Error is ' Unable to get the VLOOKUP property of the worksheet function class'
Any help please

Kind regards