Thank-you for the reply.... looking at the dates for posts, I wasn't sure that this site was still "live". I contacted Kalypso support, but a 2010 game is no longer supported by them, but Mathias had never heard of this problem either. I suspect it is an incompatiblity between Windows 10 pro, and the windows version that the game was written for. The "bug" seems persistent, and corrupts future new games. What clears this error, is delete all previous save games, AND delete all previous saved trade-routes. Though the error seems to randomly return. Which tends to suggest that the error is outside of the game coding and is endemic to an operating system incompatibilty.
In answer to your question, and it may well be MY methodology, here's how I set up my trade routes.
All of this is done at 0.1x speed, as the game can't be paused whilst editing or setting-up a new route.
Click on the required ship. Click "trade route tab", Click "new trade route button"
Plot the trade route destinations, generally 3-4 locations, with the office destination first.
Remove maintenance stop hammers from all destinations apart from office stop.
I then move ALL trade goods down to the "trade specific quantities" using the arrows to move all commodities to automatically trade, then all commodities down to "trade specific quantities" using the other down arrow.
At the office destination on the "Unload specific commodities" page, turn all commodities to "load to warehouse", using the common button at the top (rather than turning each commodity individually). Then, using the common quantity button at the top, to turn all commodities to "Max" (empty the ship to warehouse)
At the office destination on the "load specific" page, again using the button at the top, turn all commodities to "load from warehouse". The quantity of each commodity can then be set to allow you to feed the trade route from your house, customised to each trade-route.
The other destinations are then, as standard, set to, (and I will use Wood as the pricing example).... unload(sell) at 45 ( fill location to minimum required), Load (buy) at 46 ( strip location of all spare, without losing reputation). This is generally done manually, though there seems to be a "learning" routine that gets the hang of this and begins to copy your patterns on new routes created...... possibly the fault maybe this function(???)
Secondly, I have noticed the onset of this error, SEEMS to be delayed, if I manually drag each individual commodity from "don't trade" to "trade specific" without using the "move all quantities" buttons going through auto trade.
I agree with you... it's weird. What's even weirder is that no one else seems to have heard of this problem.
Does anyone else have Windows 10 pro for workstations..... version 10.0.19042.