A nasty .Net error in Visual Studio 2010 and how I fixed it

Every now and then I got a weird error whilst tinkering with some Visual Studio project files. The error was like this:

22>------ Build started: Project: myLibraryDll, Configuration: Release x64 ------
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(298,5): warning MSB8004: Intermediate Directory does not end with a trailing slash.  This build instance will add the slash as it is required to allow proper evaluation of the Intermediate Directory.
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018: The "VCMessage" task failed unexpectedly.
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018: System.FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, Object[] args)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at System.String.Format(IFormatProvider provider, String format, Object[] args)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.Shared.ResourceUtilities.FormatString(String unformatted, Object[] args)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.Utilities.TaskLoggingHelper.FormatString(String unformatted, Object[] args)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.Utilities.TaskLoggingHelper.FormatResourceString(String resourceName, Object[] args)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.Utilities.TaskLoggingHelper.LogWarningWithCodeFromResources(String messageResourceName, Object[] messageArgs)
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.CPPTasks.VCMessage.Execute()
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
22>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppBuild.targets(990,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask, Boolean& taskResult)

This is quite obscure, I think you'll agree. I eventually tracked it down to a spurious trailing slash on OutputFile. Remove it and the error goes away.

I have been bitten by this several times now so I thought if I blogged about it, then I would remember.