Yes I know how to make a dedicated server, this isn't how to make a dedicated server, this is about a problem I have launching one.
I think I know your problem, you are using an outdated dedicated server that uses a .bat extension. In the V20 update, Badspot changed on how you make a dedicated server. You no longer use the .bat file to launch one, instead you now use a shortcut that has its target box from the properties window to say at the end this: -Dedicated -Map Skylands
The easiest way for you to get this new dedicated server shortcut, is by re-installing blockland and make sure to checkmark the 'dedicated shortcuts' box while the installer is asking for which stuff you want it to install for you. The other way to make this shortcut is by right clicking Blockland and copy it. Then paste it as a shortcut on your desktop, now right click it and press properties in the menu that pops up. Now there is a box called Target, put a space into it at the very end of that box, then type in this:
-Dedicated -Map Skylands