I have had several occasions where a function (in this case Last for ticker CLX) return N/A. A retry then works and returns a valid value. I have also had this happen with symbol AIG-WT. While it seems that it is easy to manually 'recover' from this, it does mean that automated tasks are not reliable. And, even when doing manual (interactive) activities, a single N/A in a list of returned values that are then operated upon (e.g., summed) then don't work and one must look for what individual function invocation caused the problem. Are you aware of what causes this sort of erroneous response and working to fix it?