queue becomes invalid after entering event structure

[eximo]

I'm performing the exercises for the LABVIEW CORE 3 chapter 4.  It's pretty straight forward, but I started having problems and I can't explain why this is an issue.

Probes show that the queue refnum is valid before the wire enters the event structure, but becomes invalid when it enters the structure.  I even made an event case that doesn't do anything other than pass the wires through it unaltered.  Any ideas? 

[eximo]

Nevermind, I figured it out.  There isn't an option to delete my question though.

[RavensFan]

So, what was the problem?  Your answer might help someone in the future.

I don't think that picture of a very small part of your block diagram was enough for anyone to have helped you.

[eximo]

A queue will become invalid if an error causes it to be destroyed anywhere else in the code.  The pains of parallel processing.  It would be nice if LabVIEW had more information in some of the error codes.

[billko]

It could also happen if it passes through a FOR loop that iterates zero times and the wire isn't in a shift register.  An auto-indexed array that is empty will do that.  In this case, the reference going in is valid; it's the ref coming out that is just a reference with a default value of zero.  (This isn't limited to references, either.)  A shift register guarantees that what goes in the left side of a FOR loop comes out the right side.  If you thought hunting down where a reference was closed is hard to do...