It sounds like you don't have an image set properly.
I logged on and here is a shot of my buttons working:
All you are doing is switching out the image, so it will not affect the function unless you fail to properly replace the image with the exact same name.
I right clicked a player while logged it also works fine:
Regarding something being too black for your table, it sounds like the image is not transparent.
There is nothing I can do on my end if so because Image shack is altering the properties.
You can get Irfran and reset the transparency though. It is free and very quick to do.
There are instructions above.
Regarding wanting to see the empty seat, I have included an image that is transparent and only shows the word "Seat" so you can at least see where it is.
^^ (right click above)
Regarding trying to sit in an empty seat, it sounds like you have altered or removed the "SeatRT_Join" avatar.
I have not done anything for this, so you need to be sure you still have it and it is named correctly.
Regarding the chat box, meh, no way to remove it. If you delete all of the chat images, the program still displays the text box.