jsom gives me an error saying that some library is missing.

Hello everyone. i downloaded and installed josm version 5267 and installed the OpenData plugin.
When I try to open a shapefile i get this:

Could not read file ‘quebec_highway.shp’.
Error is:
java.io.IOException: java.lang.NoClassDefFoundError: java/nio/channels/SeekableByteChannel.

As far as I can see, this class(seekablebytechannel) is defined in java 7 but josm wants to run using java 6.
im using ubuntu 12.04

Please any help would be greatly appreciated.

JOSM should work with java 7, too.

I need more info to fix this bug.
Could you give me a link to download your file ? Or attach it to http://josm.openstreetmap.de/ticket/7787 ?
Does JOSM give you any stacktrace when this error happens ?