Hi Austen,
If I am reading correctly, you are trying to check B1 of 'Input + Wksheet'. The trouble is that even though you selected the sheet, the unqualified Range does not belong to the active sheet as one might expect. This is because the Range is in an object module, in this case, sheet cp1, and thus, the Range belongs to the sheet implicitly. To refer to the other sheet, you need to qualify it, regardless of what sheet is active.
Aggravatin' ain't it? I went along for the longest w/o that tidbit, until Pascal pointed it out to me one day.
Try this with a break at the top of the sub. YOu can see it happen...
Option Explicit
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Sheets("Input + Wksheet").Select
MsgBox Range("B10").Parent.Name
If Range("B10").Value = "1" Then
Sheets("CP1").Select
Range("D12").Value = "X"
Range("E25").Formula = _
"=IF(MEDCVG)=""1"",VLOOKUP(YearsOfService,Indemnity,IF(Age<=65,7,14),FALSE),0)/12"
End If
End Sub
I would note that qualifiying with the codename (If Sheet3.Range("B10").Value = 1 Then) it erred at the .Formula line. Not sure what is wrong there.
Mark