I suppose this is a bug of some sort, but I'm mainly posting because I found a clue and a way to fix it so I thought I'd pass that along.
My game was at times starting to generate a lot of "error 5: Invalid call or proceedure" error messages. That may not be word for word, but it was something close to that. In resolving a 5 day block, I'd get something like 100 of those to click through before the turn could resolve. It worked, but it was an annoying number of clicks.
A hint earlier on this pages pointed towards a fleet set to meet another fleet. It wasn't exactly my error, but it was close enough to give me a hint.
In my game, I've had fleets refueling with a jump ship that is also set as a tanker. And I realized that I'd just been shuffling these around as one was out for too long and getting bad morale, while another wasn't big enough to handle the ships I wanted to sent through.
So, I went through my fleets, and sure enough there were a couple still set to refuel with fleets that no longer existed. I've got the habit of putting ships back into shipyard TG when they are home for awhile, so the fleet list is less cluttered and I've got one place to check to see if they've had enough shore leave.
So, I think I've solved the strings of error msgs by redoing the orders on those two fleets.
If someone else has the same sort of msgs, I hope that can help them out.