Updated to Unity 5.6 from 5.4, pbxproject is now invalid?

I have a post build process step which fails to load the pbxproject saying "Exception: Invalid PBX project (parsing line 1573)", this is the block it's complaining about (I think):

B1B26327752C4F00882016D2 /* ShellScript */ = {
isa = PBXShellScriptBuildPhase;
buildActionMask = 2147483647;
files = (
);
inputPaths = (
);
outputPaths = (
);
runOnlyForDeploymentPostprocessing = 0;...

Updated to Unity 5.6 from 5.4, pbxproject is now invalid?