Android build.xml got corrupted
===

I have been on working for a while on an Android project on Eclipse.
Suddenly today when I opened Eclipse, I have seen an exclmation point near the project name, and when trying to build it, I get errors in build.xml file:

     <import file="${sdk.dir}/tools/ant/build.xml" />

    <!-- These targets only exist so they will be visible in IntelliJ. -->
    <target name="ij-debug" depends="clean,debug"/> 
    <target name="ij-release" depends="clean,release"/>
    <target name="ij-install" depends="clean">
      <exec command="ant debug install"/>
    </target>
    <target name="ij-uninstall" depends="uninstall"/>

The errors are:
  

       Cannot find ${sdk.dir}/tools/ant/build.xml imported from           
       C:\Users\myuser\Desktop\projectname\android\build.xml

and 
  

      Target clean does not exist in this project
      Target uninstall does not exist in this project

I have tried checking "ignore all buildfile problems", but then I get new errors:

    Source resource does not exist:C:\Users\myuser\Desktop\projectname\android\local.properties

Does anyone know how to resolve this issue?

Thank you.