We have customised xaml template for one of build definition and while migrating it to 64Bit.
Error Compiler error(s) encountered processing expression "BuildDetail.BuildServer.TeamFoundationServer.Uri". 'TeamFoundationServer' is not a member of 'Microsoft.TeamFoundation.Build.Client.IBuildServer'.
Try to re-add all assembly references in your code project for the template and re-build it to see whether you would get any error.
Try
buildDetail.BuildServer.TeamProjectCollection.Uri
instead ofBuildDetail.BuildServer.TeamFoundationServer.Uri
.