Server getting timed out with map

when I run my server with a map that I previously created in singleplayer and I try to log in to the server i always get "timed out" response and I am unable to get on. I also see on the server stats that the " Memory use: " is around 19mb. But when I make the server generate a new map I am able to log into the server and the memory use is around 70mb.
My question is why do i get "timed out"?
Does it have something to do with the "Memory use"?
How can I increase it if possible?