I have a problem since a few days. I tried to send resources (mainly crop) to another player of my kingdom. However, on a certain moment the market place only lets me send a very small amount. I thought this was a daily limit, but few days later I am still not able to send him anything. Is this a bug?
It's not a daily limit, it is a set limit. Once you are at your limit, you can only send more to him once he sends some to you, or your troops eat his crop via reinforcing him or something.