Try to remove all the items in your store one by one and put them into your inventory then try to close it, don't forget to go retrieving your items to Fredrick if you sold items. Try to click on "organize" until your store is empty. Also if you sold more than 2.1b, you need to have 0 mesos on your character for retrieving them. So put your mesos in your storage. Make sure to have slots in your inventory tab also. If it doesn't work then wait for @alex answer.