I want to use INVEdit in Multiplayer how do i do it? i am running windows 7 64 bit and when i try to open server_level.dat or level.dat it comes up with the following error:

System.Exception: Can't Find Inventory tag. at INVEdit.Mainform.Open(Page page, String file)

I hope I can get a reply soon enough. also, how do i use Omen to make a base for my map? when i open the same files (server_level.dat or level.dat) it comes up with this message in the box:

(This is for server_level.dat)
Unable to find the level class. Check whether minecraft-server.jar is in your classpath.
(Btw it is)

(level.dat)
Unsupported file type. Level not loaded.10 0 0 10

I would apreciate some help on how to run omen or INVEdit or if you have any other programs that can help me make my own server. thanks.
Vulkara_1997