igarant , when a new release comes out, its best to rebuilt your server from scratch......
click the jar, wait for the extraction.........then run the server, stop the server. insert your own world.put your banplayers +ban ips+ops files in
keep making backups of the whole server folder (with winrar for example).
then you can always go back to a working version of your server
then put the build 250 in coremods and see if it makes a plugins folder.