Can't sell stock anymore.

Hi all,

I'm very new to the game, so I'm sure I'm just doing something dumb/misunderstanding the rules, but I'm sure I used to be able to sell stock at the start of the game for seed money to upgrade my base. Now however, whenever I try to sell stock I just this error noise and I cannot sell. It appears that the AI can still sell, but I can't. In addition it doesn't look like I can sell stock at any point in the game.

I have tried this on different levels of difficulty, with different credit ratings (AAA - D), with different custom settings and with different maps. Nothing makes a difference. Could someone point me to what I'm doing wrong, please?

Thanks muchly!