whats the minimum?

i'm placing 35,000 troops, 15,000 turrets, 500 tanks, and 35,000 bushels on the market

Minimum size of Food, Oil, and Military sales is 5000 units. 500 Tanks wont cut it.

Judging by your post it sounds like you're running a "rainbow" country. If that's the case you may want to look into specializing your country build to maximize your growth and NW potential.

I suppose it's possible you're doing some sort of indy/farm hybrid start... but that's probably not optimal.

http://wiki.earthempires.com/index.php/Strategies

minimum is 5k of those goodies you don't have on market so if you have 20k troops available but 1k on market unsold then you can't sell troops.