Many people (myself included) have / had trouble using the Trading Post or Black Market on Windows Vista+.
But it is very easy to solve the problem!
1) Go to the folder where you saved the game.
2) Right-click on the executable.
3) Go into properties.
4) In the compatibility tab, check the “Run this program as administrator”
5) Click OK and you’re done, now you no longer have problems with the Trading Post / Black Market
I hope helped!