Please, tell us what presets you use, your system info (first three paragraphs Help -> Show status report) and add the whole exceptions details and not just the first line.
Thanks
Can not reproduce with "NewTags" and "steps" presets. Both messages close after clicking "OK".
Using /usr/lib/jvm/java-6-openjdk/bin/java to execute josm.
Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2012-02-15 02:32:11
Last Changed Author: xeen
Revision: 4934
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2012-02-15 02:44:53 +0100 (Wed, 15 Feb 2012)
Last Changed Rev: 4934
Warning: failed to read MOTD from 'http://josm.openstreetmap.de/wiki/StartupPage'. Exception was: java.net.UnknownHostException: josm.openstreetmap.de
java.net.UnknownHostException: osmtools.de
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:175)
at java.net.Socket.connect(Socket.java:546)
at sun.net.NetworkClient.doConnect(NetworkClient.java:169)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:409)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:530)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:240)
at sun.net.www.http.HttpClient.New(HttpClient.java:321)
at sun.net.www.http.HttpClient.New(HttpClient.java:338)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:935)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:876)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:801)
at org.openstreetmap.josm.io.MirroredInputStream.connectFollowingRedirect(MirroredInputStream.java:275)
at org.openstreetmap.josm.io.MirroredInputStream.checkLocal(MirroredInputStream.java:220)
at org.openstreetmap.josm.io.MirroredInputStream.<init>(MirroredInputStream.java:79)
at org.openstreetmap.josm.io.MirroredInputStream.<init>(MirroredInputStream.java:40)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readAll(TaggingPreset.java:1187)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readAll(TaggingPreset.java:1214)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readFromPreferences(TaggingPreset.java:1250)
at org.openstreetmap.josm.gui.preferences.TaggingPresetPreference.initialize(TaggingPresetPreference.java:260)
at org.openstreetmap.josm.Main.<init>(Main.java:279)
at org.openstreetmap.josm.gui.MainApplication.<init>(MainApplication.java:64)
at org.openstreetmap.josm.gui.MainApplication.main(MainApplication.java:253)
java.net.UnknownHostException: josm.openstreetmap.de
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:175)
at java.net.Socket.connect(Socket.java:546)
at sun.net.NetworkClient.doConnect(NetworkClient.java:169)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:409)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:530)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:240)
at sun.net.www.http.HttpClient.New(HttpClient.java:321)
at sun.net.www.http.HttpClient.New(HttpClient.java:338)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:935)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:876)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:801)
at org.openstreetmap.josm.io.MirroredInputStream.connectFollowingRedirect(MirroredInputStream.java:275)
at org.openstreetmap.josm.io.MirroredInputStream.checkLocal(MirroredInputStream.java:220)
at org.openstreetmap.josm.io.MirroredInputStream.<init>(MirroredInputStream.java:79)
at org.openstreetmap.josm.io.MirroredInputStream.<init>(MirroredInputStream.java:40)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readAll(TaggingPreset.java:1187)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readAll(TaggingPreset.java:1214)
at org.openstreetmap.josm.gui.tagging.TaggingPreset.readFromPreferences(TaggingPreset.java:1250)
at org.openstreetmap.josm.gui.preferences.TaggingPresetPreference.initialize(TaggingPresetPreference.java:260)
at org.openstreetmap.josm.Main.<init>(Main.java:279)
at org.openstreetmap.josm.gui.MainApplication.<init>(MainApplication.java:64)
at org.openstreetmap.josm.gui.MainApplication.main(MainApplication.java:253)
loading plugin 'turnlanes' (version 27676)
loading plugin 'reverter' (version 27676)
RemoteControl: adding command "revert_changeset" (handled by RevertChangesetHandler)
loading plugin 'utilsplugin2' (version 27710)