Bublina,
Check the error out of the "Preview Queue Element" function when you have the problem.
(You'll have to create a wire going to the Case structure to probe or create an indicator.)
My guess is that you have Automatic Error Handling turned off (VI Properties -> Execution).
If this is true, you wont see an error with Highlighting turned on.
You should not turn off Automatic Error Handling unless you are going to handle the errors yourself.
Since you didn't wire the Error Out terminal, you would be ignoring errors from that function (not recommended).
For example: If the queue reference is not valid, you will get exactly the results you are seeing.
The attached vi (LV 2012) illustrates the effects of a bad queue reference.
steve
