automation error catastrophic failure with user check code on open - vba

Question

I have some VBA code that checks a person's job title before allowing someone to edit the document. After adding this code in I occasionally get an "Automation Error Catastrophic Failure" message only when opening the spreadsheet. As far as I can tell it does not damage any part of the workbook, and you just have to exit the command debugger twice before it opens. Obviously others at work see this message and overreact to it. Please see my functions that activate when opening the workbook.
Private Sub Workbook_Open()
Sheets("Start Here").Select
Range("A3").Select
End Sub
Private Sub Worksheet_Activate()
If Usercheck() = True Then
ProtectionOff
Else
ProtectionOff
Range("A1:V260").Locked = True
ProtectionOn
End If
End Sub
Function Usercheck() As Boolean
Dim user As String
Dim title As String
On Error GoTo ErrorHandler
user = UserName()
title = WorksheetFunction.VLookup(user,
Sheets("BaseTables").Range("tblStaff[[#All],[Username]:[Title1]]"), 2, False)
If Left(title, 20) = "Technical Specialist" Then
Usercheck = True
ElseIf Left(title, 19) = "Engineering Manager" Then
Usercheck = True
ElseIf Left(title, 9) = "Team Lead" Then
Usercheck = True
Else
Usercheck = False
End If
Exit Function
ErrorHandler:
Usercheck = False
End Function
Public Function UserName()
UserName = Environ$("UserName")
End Function