Host OS: Windows 7 Pro 64 bit SP 1
SDK tools version (available in the "About" section of the 'android' tool
UI): 21.0.1
Eclipse version: 3.8.0
ADT plug-in version: ADT v21.0.1-543035
Platform targeted by your project: 8
Version of the platform running in the emulator: (emulator not used)
I have downloaded the latest ADT bundle for Windows x86_64 from http://developer.android.com/sdk/index.html today (December 29th 2012).

STEPS TO REPRODUCE:
1. Create new android application, call it foobar, set it to use API level 8 and select default choices in wizard
2. Close and open Eclipse and verify that project builds with no errors
3. Open the src folder in Windows Explorer
4. Create a folder called .svn (you need to use the command line for this) and set it to hidden.
5. Open the .svn folder and add a file (call it entries with no extension)
6. Refresh the foobar project
7. Close and open Eclipse
8. Build of project will fail

EXPECTED RESULTS:
Subversion is a widely used for source control. I have used it with earlier versions of the Android SDK and Eclipse with no problems, so the build of the project should succeed.

OBSERVED RESULTS:
A pop-up notifying of an error during the build. Pressing Details reveals the following message:

Errors occurred during the build.
Errors running builder 'Android Pre Compiler' on project 'foobar'.
java.lang.NullPointerException

ADDITIONAL INFORMATION:
A workspace with a sample project has been attached.

Output from .log:
!SESSION 2012-12-29 00:37:36.223 -----------------------------------------------
eclipse.buildId=v21.0.1-543035
java.version=1.6.0_37
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_GB
Framework arguments: -product com.android.ide.eclipse.adt.package.product
Command-line arguments: -os win32 -ws win32 -arch x86_64 -product com.android.ide.eclipse.adt.package.product

!ENTRY com.android.ide.eclipse.ddms 4 0 2012-12-29 00:37:41.741
!MESSAGE DDMS files not found: C:\Development\eclipse\platform-tools\adb.exe C:\Development\eclipse\tools\hprof-conv.exe C:\Development\eclipse\tools\traceview.bat

!ENTRY com.android.ide.eclipse.adt 4 0 2012-12-29 00:38:16.281
!MESSAGE Failed to load properties file for project 'foobar'
!SESSION 2012-12-29 00:39:21.319 -----------------------------------------------
eclipse.buildId=v21.0.1-543035
java.version=1.6.0_37
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_GB
Framework arguments: -product com.android.ide.eclipse.adt.package.product
Command-line arguments: -os win32 -ws win32 -arch x86_64 -product com.android.ide.eclipse.adt.package.product

!ENTRY com.android.ide.eclipse.adt 4 0 2012-12-29 00:39:31.877
!MESSAGE Failed to finish PrecompilerBuilder#startupOnInitialize()
!STACK 0
java.lang.NullPointerException
at com.android.ide.eclipse.adt.internal.build.SourceProcessor.scanFolderForSourceFiles(SourceProcessor.java:374)
at com.android.ide.eclipse.adt.internal.build.SourceProcessor.scanFolderForSourceFiles(SourceProcessor.java:380)
at com.android.ide.eclipse.adt.internal.build.SourceProcessor.buildSourceFileList(SourceProcessor.java:353)
at com.android.ide.eclipse.adt.internal.build.SourceProcessor.<init>(SourceProcessor.java:97)
at com.android.ide.eclipse.adt.internal.build.SourceProcessor.<init>(SourceProcessor.java:113)
at com.android.ide.eclipse.adt.internal.build.AidlProcessor.<init>(AidlProcessor.java:85)
at com.android.ide.eclipse.adt.internal.build.builders.PreCompilerBuilder.startupOnInitialize(PreCompilerBuilder.java:800)
at org.eclipse.core.internal.events.BuildManager.getBuilder(BuildManager.java:542)
at org.eclipse.core.internal.events.BuildManager.getBuilder(BuildManager.java:567)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:237)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:292)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:295)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:351)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:374)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:143)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:241)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)

!ENTRY org.eclipse.core.resources 4 2 2012-12-29 00:39:35.432
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.core.resources".
!STACK 0
java.lang.NullPointerException
at com.android.ide.eclipse.adt.internal.build.builders.PreCompilerBuilder.build(PreCompilerBuilder.java:673)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:728)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:199)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:239)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:292)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:295)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:351)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:374)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:143)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:241)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)

!ENTRY org.eclipse.core.resources 4 75 2012-12-29 00:39:35.452
!MESSAGE Errors occurred during the build.
!SUBENTRY 1 com.android.ide.eclipse.adt 4 75 2012-12-29 00:39:35.452
!MESSAGE Errors running builder 'Android Pre Compiler' on project 'foobar'.
!STACK 0
java.lang.NullPointerException
at com.android.ide.eclipse.adt.internal.build.builders.PreCompilerBuilder.build(PreCompilerBuilder.java:673)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:728)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:199)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:239)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:292)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:295)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:351)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:374)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:143)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:241)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)