Why is Eclipse (Galileo) suddenly giving me a slew of Error Messages?

Which error message it lists in the Error window even when all I do is close a Java source window.

They start with "Unable to read repository at http://download.aptana.org/tools/studio/plugin/install/xul-eclipse" followed with several other repository read failures, followed by:

NLS unused message: missingOneOfTwoAttributes in:
org.eclipse.wst.common.project.facet.core.internal.FacetedProjectFrameworkImpl

with Session data (From Event Details):

eclipse.buildId=java.version=1.6.0_17
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86, WS=gtk, NL=en_US
Framework arguments:  -product org.eclipse.epp.package.java.product
Command-line arguments:  -os linux -ws gtk -arch x86
-product    org.eclipse.epp.package.java.product

Several more similar NSL unused messages, and then "Project facet wst.web has not been defined. It is used in plugin org.eclipse.jst.common.project.facet.core."

All this started after I made a trivial change to Android source code in one project, and 开发者_如何转开发now every other Android project I try to build (even if only whitespace changed) fails with the same failure: the little red box indicating a build error (with a white cross inside) decorates the project folder, but NO similar error is indicated on ANY of the subfolders.