Private Sub Okbutton_Click()

'Make Sheet1 Active
Sheets(1).Activate

'Export Data to worksheet
Cells(2, 5).Value = tbunder.Value
Cells(2, 6).Value = cbunderxp.Value
Cells(2, 3).Value = tvvolbeta.Value
Cells(2, 4).Value = tbedge.Value
Cells(2, 10).Value = tbus.Value
Cells(2, 7).Value = tbuc.Value
Cells(2, 18).Value = tbup.Value
Cells(2, 34).Value = tbhedge.Value
Cells(2, 35).Value = cbhxp.Value
Cells(2, 41).Value = tbhc.Value
Cells(2, 54).Value = tbhp.Value
Cells(2, 17).Value = tbucp.Value
Cells(2, 27).Value = tbupp.Value

'Import data from work sheet

tbhs.Value = Cells(2, 68).Value
tbhcp.Value = Cells(2, 43).Value
tbhpp.Value = Cells(2, 59).Value

'Add trade to positions sheet
Sheets("Positions").Select
Rows("4:4").Select
Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
Range("A5:V5").Select
Selection.AutoFill Destination:=Range("A4:V5"), Type:=xlFillDefault
Range("A4:V5").Select

End Sub

Private Sub UserForm_Initialize()

'Underlying Security
tbunder.Value = ""
'Underlying security expiration combobox
With cbunderxp
.AddItem "'3/17/2012"
.AddItem "'4/21/2012"
.AddItem "'5/19/2012"
.AddItem "'6/16/2012"
.AddItem "'7/21/2012"
.AddItem "'8/18/2012"
.AddItem "'9/22/2012"
.AddItem "'10/20/2012"
End With

'Underlying security call
tbuc.Value = ""
'Underlying security put
tbup.Value = ""
'Underlying security size
tbus.Value = ""
'Vol Beta
tvvolbeta = ""
'Expected Edge
tbedge = ""
'Hedging Security
tbhedge = ""
'Hedging Expiriation
With cbhxp
.AddItem "'3/17/2012"
.AddItem "'4/21/2012"
.AddItem "'5/19/2012"
.AddItem "'6/16/2012"
.AddItem "'7/21/2012"
.AddItem "'8/18/2012"
.AddItem "'9/22/2012"
.AddItem "'10/20/2012"
End With
'Hedge call
tbhc = ""
'Hedge put
tbhp = ""
'Hedge size
tbhs.Value = ""
'Underlying Call Price
tbucp = ""
'Underlying Put Price
tbupp = ""

End Sub

This keeps happening when the Userform tries to import data from the worksheet into the form. What does this error mean? What causes it? and how do i fix it?