I am getting a 500 server error when I Queue mailings to 1 of my 10 lists on Gossamer List. This list has the most subscribers at 15,000. Please tell me any way to fix this, any settings to check. I am "almost" sure I got everything right as mailings work to every other list except this one. And to be sure I imported the subescribers correctly, I broke the list into 15 lists of 1,0000 subscribers and imported each text file separately.

thanks