Same Problem too, and i've been running a server since the middle of the year and suddenly i try the latest build and it says it cannot access the .jar file. I am gonna try to use a older build and see if that helps any. :/
Ok i just tried a older build and it won't work, so it must be something with the computer that changed.
Now i just tried my older server that i havn't updated yet and it worked..... im confused.