Simple builds for Android keep failing with unauthorized exceptions.

I have been tearing my hair out trying to get Unity to do a simple build of a game for Android - always getting the same error (with any game) - see below.

UnauthorizedAccessException: Access to the path "...mygame\Temp\StagingArea\res\values\strings.xml" is denied. System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/FileStream.cs:320) System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share) (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare) System.Xml.XmlTextWriter..ctor (System.String filename, System.Text.Encoding encoding) UnityEditor.AndroidXmlDocument.SaveAs (System.String path) UnityEditor.AndroidXmlDocument.Save () UnityEditor.Android.PostProcessor.Tasks.PrepareAPKResources.PatchStringsXml () UnityEditor.Android.PostProcessor.Tasks.PrepareAPKResources.Execute (UnityEditor.Android.PostProcessor.PostProcessorContext context) UnityEditor.Android.PostProcessor.PostProcessRunner.RunAllTasks (UnityEditor.Android.PostProcessor.PostProcessorContext context) UnityEditor.Android.PostProcessAndroidPlayer.PostProcess (BuildTarget target, System.String stagingAreaData, System.String stagingArea, System.String playerPackage, System.String installPath, System.String companyName, System.String productName, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) UnityEditor.Android.AndroidBuildPostprocessor.PostProcess (BuildPostProcessArgs args) UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTargetGroup targetGroup, BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:271) UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

This error has been noted before in a previous posting : https://forum.unity.com/threads/access-to-the-path-c-temp-staging_area-res-values-strings-xml-is-denied.433124/ but without a definite analysis of the problem and work around solution.

Versions: Android SDK 3.1.3, Java JDK jdk1.8.0_171, Unity 2017.2.0f3

Even deleting the Temp and Library directories and rebuilding does not cure the problem.

The file in question, strings.xml is read-only which explains the error message. The question is what template was used by Unity to create that strings.xml file. The template file must be read-only and I need to unset the readonly attribute.

But where is this template? Although the Unity source code for Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs is available for scrutiny I cannot find source code for Unity Android AndroidBuild etc.

Any help at all would be appreciated?

Nigel & Jules