To Eliminate "Run-time Error 13" Message

I have used a process of elimination by disabling all VBA code and macros throughout this workbook systematically until I traced my problems to this code.

Private Sub Worksheet_Calculate()
Dim red1TargetCell As Range
Dim red1dblValue As Double
Set red1TargetCell = Sheets("1-A").Range("AC3")
red1dblValue = Val(red1TargetCell.Value)
Select Case red1dblValue
Case 1
Call Red1copypricelog
End Select
End Sub

This code is delivering an error message when the workbook is first opened that reads as follows:

Run-time error "13"
Type mismatch

I can answer "end" to the debug box that appears and the code runs as if there are no problems. I have this code applied to 7 different worksheets within the workbook with slightly altered variable names, so I have to click "end" seven times and then the workbook functions as if all is OK. One other note worthy point is when I have this workbook open, it locks up if I try to open any other excel files at the same time. I want to make sure all my code and macros within this workbook only work within this same workbook. I'm assuming that is why other workbooks are locking up. I may be way off here since my VBA programming is very limited.