BACKGROUND: I am trying to identify how many unique time periods I have from a list of dates that have. Elsewhere, I have seen a method which utilizes collections and error trapping (right term? I mean "On Error Resume Next" in any case) to build the collection with unique values. I have even used this structure successfully in other code that I have written, but in my current circumstance, I am getting an "Error 457: This key is already associated with an element of this collection." Thinking I was using the collection incorrectly, I opened up some older code I wrote 6 months ago (on a different computer for a different company) which uses the same structure and was known to WORK. This older code broke on the same identical error, which it previously did not do. Here is the sample of my work-in-progress code:
Dim rng as range
Dim TimePeriod as Collection
Set TimePeriod = New Collection
For Each rng In Range("I2:I6")
On Error Resume Next
TimePeriod.Add rng.Value, CStr(rng.Value) 'This is where the code breaks
On Error GoTo 0
Next rng
QUESTION: I'm wondering if there is a setting or a reference library that I am somehow missing that is causing both pieces of code to break, or how to determine that, since both codes are functionally identical, and the previously tested satisfactory code breaks like my work-in-progress. I expected the "On Error Resume Next" to force the loop to pass over the error. Any suggestions?
--Update--
Sample data in range("I2:I6") as follows:
1/21/15
1/21/15
1/21/15
1/23/15
1/27/15