TFS MsBuild and Web Deployment Project randomly fail

We have a build running on a TFS2008 build server and one of the builds 开发者_开发知识库has started failing. It looks as if the aspnet_compile step of the Web Deployment project (wdproj) has stopped producing the App_Global.asax.compiled file.

After a few builds it starts to work again, until a few builds later, the problem is back. If I run the tools manually, it works fine.

It is occuring on all the branches with the module, and not code changes have been made that is common to all the modules. The problem exists on both build servers. I've compared the build directory structures for a successful and failing build, and they only differ by the file above (and the next step, which relies on the App_Global.asax.compiled file (this is the aspnet_merge step))

Any ideas?

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Turns out the most likely culprit is NTFS compression… weird