A tunneled Excel refnum goes from a valid value to a NULL between iterations of a For Loop?

Question

How would a tunneled Excel refnum go from a valid value to a NULL between iterations of a For Loop?
For
some reason this works find in one VI and when executed and not in
another.  Here's screen shots of the highlighted execution with probes
appropriately. The "Open" refnum is passed into "Performance Test -
Write Data To Files.vi".  That's where the trouble is.  You can see
that it goes into the For Loop.  The first iteration is okay, but the
second and subsequent iterations have the refnum NULL.  See images
below.
(I don't know how to delete an accidental double post, sorry)
Message Edited by James DiLiberto on 01-22-2008 01:48 PM
Attachments:
Second Iteration1.jpg ‏158 KB
First Iteration1.jpg ‏145 KB
Second Iteration Error Dialog1.jpg ‏20 KB

Answer 1

Is there any chance that the Insert Data Into Excel VI is closing the reference or that it is closed anywhere else (e.g. through a local or by having its owner destroyed)?
I wouldn't expect the numeric value of the reference to change to 0, but since ActiveX is an external resource, I suppose that it's possible that the probe shows the number only if the resource is actually accessible.
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