"Due to rapidly changing partner availability the following flights are no longer available. Please choose another flight or modify your search criteria."

Yes, I'm asking a lot - booking a complex award itinerary to Africa via a few different *A carriers. The UA search engine fails to function when the same flights show up as available on a daily basis, only to be phantoms when I attempt to book them. ET and MS are specifically the problems as far as I my amateur eye can discern. Yet to have no functional search engine makes this very, very frustrating. Expertflyer is linked into the UA system so this doesn't help, either. My least worst option is to just call daily? Is there a time at which ET and/or MS open up inventory?

Any advice? What's the best *A search engine?

Thank you.