[news.eclipse.newcomer] why I keep getting this error message("Errors du

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Hi,

I have created an Eclipse project from existing source. After it is
done, there is no red error signal at all. Everything seems fine.

But once in several minutes, a pop window always shows up, saying

Errors during build
 Errors running builder "Intergrated External Tool Builder" on project
myProject.
 Variable references non-existent resource:
${workspace_loc:/myproject/build.xml}

I click the OK button and the window is gone. But when I edited a Java 
file and hit "Control-s", it comes back again. It is annoying.

My guess is that somehow Eclipse is executing myproject/build.xml and
this build.xml has an error?

In the shell terminal, if I type "ant compile-all" to run the target in
build.xml, it is successfully done, which means everything can be
compiled. If I ran "ant test" to run the test target in build.xml, some
tests are failing. But is this related to the pop window keep coming back?

Thank you very much.