User-defined function appears to be preventing Worksheet_Change trigger?

I have the following user-defined function, which works independently (that is, it does what it is supposed to):

Function ActivityIndex(currentDate As Date, projectName As String _
, firstRow As Integer, lastRow As Integer)

End Function

However, since I have added it to my worksheet, my Worksheet_Change sub no longer works:

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Row = 1 And Target.Column = 3 Then
Call UpdateLink("E1", "Project View")
Call GetDates
Call ResetDate("Project View", "Weighting", 56, 5)
Call ResizeFont
End If
End Sub

Every part of the Worksheet_Change worked before I started calling my function ACTIVITYINDEX from cells on the worksheet.

Is it possible that, because it is called from a cell, ACTIVITYINDEX is also being called with every Worksheet_Change trigger and somehow out-competing my Worksheet_Change sub

Is it the Worksheet_Change that needs EnableEvents turned off, or is it my function

Edit: I tried it with both, and either way I recieved "Compile Error: Invalid Use of Property"

Edit2: Missing an =, but when i fixed it, either way it's still not running my Workbook_Change.

None of the routines I call use ActivityIndex.

If I comment out the ActivityIndex function (turning all the uses in Excel formulas to #NAME! errors), it will run properly after resetting EnableEvents to true (see below):

I've made some progress:

Using the immediate window, I determined that ActivityIndex was mysteriously turning EnableEvents to false. I fixed this by adding Application.EnableEvents = true to the last line without any = false at the top. This still wasn't running my Calls in Worksheet_Change properly, but at least I could get a MsgBox to pop whenever I changed the sheet.

I moved the call for UpdateLink before the IF statement and added a MsgBox debug downstream. My MsgBox doesn't pop after the call to UpdateLink, nor does UpdateLink work properly (it worked properly before.) After UpdateLink gets called, the immediate window tells me EnableEvents is still true, but it doesn't work and it doesn't allow anything downstream.

Code: