NoClassDefFoundError: Could not initialize class com.sun.imageio.plugins.jpeg.JPEGImageReader

[anonymous]

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2013-04-09 01:34:26
Last Changed Author: stoecker
Revision: 5836
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2013-04-07 23:18:22 +0200 (Sun, 07 Apr 2013)
Last Changed Rev: 5836

Identification: JOSM/1.5 (5836 it) Windows 7
Memory Usage: 81 MB / 247 MB (22 MB allocated, but free)
Java version: 1.7.0_17, Oracle Corporation, Java HotSpot(TM) Client VM
Operating system: Windows 7
VM arguments: [-Duser.home=E:\PortableApps\JavaPortableLauncher\Data\AppData]
Dataset consistency test: No problems found

Plugin: DirectDownload (29435)
Plugin: ElevationProfile (29435)
Plugin: buildings_tools (29435)
Plugin: continuosDownload (28565)
Plugin: imagery_offset_db (29467)
Plugin: imageryadjust (29435)

java.lang.NoClassDefFoundError: Could not initialize class com.sun.imageio.plugins.jpeg.JPEGImageReader
	at com.sun.imageio.plugins.jpeg.JPEGImageReaderSpi.createReaderInstance(Unknown Source)
	at javax.imageio.spi.ImageReaderSpi.createReaderInstance(Unknown Source)
	at javax.imageio.ImageIO$ImageReaderIterator.next(Unknown Source)
	at javax.imageio.ImageIO$ImageReaderIterator.next(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at javax.imageio.ImageIO.read(Unknown Source)
	at org.openstreetmap.gui.jmapviewer.Tile.loadImage(Tile.java:170)
	at org.openstreetmap.gui.jmapviewer.OsmFileCacheTileLoader$FileLoadJob.loadOrUpdateTile(OsmFileCacheTileLoader.java:235)
	at org.openstreetmap.gui.jmapviewer.OsmFileCacheTileLoader$FileLoadJob.run(OsmFileCacheTileLoader.java:171)
	at org.openstreetmap.gui.jmapviewer.JobDispatcher$JobThread.executeJobs(JobDispatcher.java:168)
	at org.openstreetmap.gui.jmapviewer.JobDispatcher$JobThread.run(JobDispatcher.java:135)

[Don-vip]

This is related to your Java configuration.
You may try to update to latest version (1.7.0_21 at this time) and/or use the standard version instead of the portable one.