I am having a program bug that makes absolutely no sense to me.

First issue: The program runs fine most of the time (it is a desktop gadget-type program that updates itself every few hours). However, this is the second time (over the past months) that it threw an error.

Second issue: When I shut the program down and restart it, I get the same error. However, when I open it in Visual Studio and run it, no error.

Here is the error:
Index was outside the bounds of the array.
at xxx.vb: Line1
at xxx.vb: Line2
at xxx.vb: Line3

But this makes no sense at all:
Line1: Dim currentMonth As Integer = DateTime.Now.Month (this line of code is in SubOne)
Line 2: Dim myDocFor As New XDocument (this line of code is in SubTwo, but SubOne is called three lines after this)
Line 3: SubTwo()

What the heck is going on???

Note: Typing this up took about ten minutes and the program is again running properly. In case it matters, it is about 5:00 pm local time.