NoSuchMethodError with GWT

I had a GWT app that was working fine. Then I added guava-r09.jar and guava-r09-gwt.jar, and messed around with the build path a bit. Now, when I try to launch my app in hosted mode, I get this error:

Caused by: java.lang.NoSuchMethodError: java.util.Set.java_lang_Iterable_iterator()Ljava/util/Iterator;
    at com.google.gwt.user.cellview.client.CellBasedWidgetImpl.sinkEvents(CellBasedWidgetImpl.java:117)
    at com.google.gwt.user.cellview.client.AbstractHasData.(AbstractHasData.java:279)
    at com.google.gwt.user.cellview.client.CellList.(CellList.java:211)
    at com.google.gwt.user.cellview.client.CellList开发者_开发百科.(CellList.java:175)
    at com.my.client.myMainView.(MainView.java:33)

I have found various sites that propose solutions (Tim Mattisson's blog and ForgetMeNotes). I took the advice they listed there (re-ordering the build path), but my problem persists. What could I be doing wrong?