This is not what you want to see in your MSBuild log:
This unwelcome tale appeared in my log because I had this Target in the project file:
<Target Name="DeleteOldResultFiles"> <ItemGroup> <LogFile Include="$(ReportsDirectory)\*.*"/> </ItemGroup> <Delete Files="@(LogFile)" TreatErrorsAsWarnings="true"/> </Target>
Unfortunately, I had miss-typed the $(ReportsDirectory) property as $(ReportDirectory), and said miss-typed property did not exist, so MSBuild was defaulting to the empty string. Thus the LogFile Item was being populated with a list of all the files in my C:\ drive, and the Delete task was obediently purging them.
The moral of this story: don't run MSBuild as Admin - or if you're as foolish as I was, make sure you've at least got a cloned Virtual machine (as I had) from which to copy any files which might get trashed.