VBA -Excel form <Subscript out of range> - excel

Question

I am trying to add a button command to save data to ta table in excel. I get Error:9: Subscript out of range. I don't know how to fix it. The data entry sheet in my work book is called "Studies"
Here is the code:
Private Sub CommandButtonSave_Click()
Dim iRow As Long
Dim iCode As Long
Dim ws As Worksheet
Set ws = ThisWorkbook.Sheets("Studies")
'find first empty row in database
iRow = ws.Cells.Find(What:="*", SearchOrder:=xlRows, _
SearchDirection:=xlPrevious, LookIn:=xlValues).Row + 1
iCode = Me.txtcode.Value
'check for a part number
If Trim(Me.txtcode.Value) = "" Then
Me.txtcode.SetFocus
MsgBox "Please enter study"
Exit Sub
End If
'copy the data to the database
ws.Cells(iRow, 1).Value = Me.txtcode.Value
ws.Cells(iRow, 2).Value = Me.cboreport.Value
ws.Cells(iRow, 3).Value = Me.txttitle.Value
ws.Cells(iRow, 4).Value = Me.cboprincipalinvestigator.Value
ws.Cells(iRow, 5).Value = Me.txtstartdate.Value
ws.Cells(iRow, 6).Value = Me.txtenddate.Value
ws.Cells(iRow, 7).Value = Me.cbotreatment.Value
ws.Cells(iRow, 8).Value = Me.cboSSI.Value
ws.Cells(iRow, 9).Value = Me.cbolotnumber.Value
ws.Cells(iRow, 10).Value = Me.cbodilution.Value
ws.Cells(iRow, 11).Value = Me.cbofrequency.Value
ws.Cells(iRow, 12).Value = Me.cbotmethodofinduction.Value
ws.Cells(iRow, 13).Value = Me.cbostartday.Value
ws.Cells(iRow, 14).Value = Me.cboendday.Value
ws.Cells(iRow, 15).Value = Me.cbodiseasemodel.Value
ws.Cells(iRow, 16).Value = Me.cbodose.Value
ws.Cells(iRow, 17).Value = Me.cbommethodofinduction.Value
ws.Cells(iRow, 18).Value = Me.cbobleedpoints.Value
ws.Cells(iRow, 19).Value = Me.cbotakedownpoints.Value
ws.Cells(iRow, 20).Value = Me.cboimmunecells.Value
ws.Cells(iRow, 21).Value = Me.cbochemotoxins.Value
ws.Cells(iRow, 22).Value = Me.cbocellmarkers.Value
ws.Cells(iRow, 23).Value = Me.cboqpcr.Value
ws.Cells(iRow, 24).Value = Me.cbotissue.Value
ws.Cells(iRow, 25).Value = Me.cboother.Value
ws.Cells(iRow, 26).Value = Me.cbostrain.Value
ws.Cells(iRow, 27).Value = Me.cbosupplier.Value
ws.Cells(iRow, 28).Value = Me.txtdateofbirth.Value
ws.Cells(iRow, 29).Value = Me.txtfindings.Value
ws.Cells(iRow, 30).Value = Me.cbotechnicalissues.Value
ws.Cells(iRow, 31).Value = Me.cbokeyword.Value
ws.Cells(iRow, 32).Value = Me.txtnotes.Value
'clear the data
Me.txtcode.Value = ""
Me.cboreport.Value = ""
Me.txttitle.Value = ""
Me.cboprincipalinvestigator.Value = ""
Me.txtstartdate.Value = ""
Me.txtenddate.Value = ""
Me.cbotreatment.Value = ""
Me.cboSSI.Value = ""
Me.cbolotnumber.Value = ""
Me.cbodilution.Value = ""
Me.cbofrequency.Value = ""
Me.cbotmethodofinduction.Value = ""
Me.cbostartday.Value = ""
Me.cboendday.Value = ""
Me.cbodiseasemodel.Value = ""
Me.cbodose.Value = ""
Me.cbommethodofinduction.Value = ""
Me.cbobleedpoints.Value = ""
Me.cbotakedownpoints.Value = ""
Me.cboimmunecells.Value = ""
Me.cbochemotoxins.Value = ""
Me.cbocellmarkers.Value = ""
Me.cboqpcr.Value = ""
Me.cbotissue.Value = ""
Me.cboother.Value = ""
Me.cbostrain.Value = ""
Me.cbosupplier.Value = ""
Me.txtdateofbirth.Value = ""
Me.txtfindings.Value = ""
Me.cbotechnicalissues.Value = ""
Me.cbokeyword.Value = ""
Me.txtnotes.Value = ""
Me.txtstartdate.Value = Format(Date, "Medium Date")
Me.txtenddate.Value = Format(Date, "Medium Date")
Me.txtdateofbirth.Value = Format(Date, "Medium Date")
Me.txtcode.SetFocus
End Sub