Hi Its my fault that all the builtbots have broken, so I thought I'd post including the reasons why - and asking for how to fix it. The reason is that I've now introduced a dependency on Data.Binary - which is definately the right thing to do (before we were using our own Binary instances). Data.Binary depends on Data.ByteString. The problem is that Data.ByteString is available as a library in base on GHC 6.6, but not on 6.4 - where you have to use fps. So basically, we can say Yhc is GHC 6.6 only, or we can make the build system download and use fps, which would be rather annoying, or we can ask the Yhc users to install fps on their own for 6.4. Or we can ask the ByteString developers how to clean up what looks like a bad case of DLL hell. Thanks Neil