It looks like Linux Integration Services 3.4 only copes with Centos 6.3 with kernel 2.6.32-279.9.1.el6.i686 or older. It's odd that
Microsoft officially supports Centos 6, but their integration software never seems to keep up with the kernels (I hit a similar issue with 3.3). Thankfully it's not too difficult to tell grub.conf to boot the older version (or add kernel* as an exclusion in yum.conf), assuming you can access the Hyper-V host okay, but it's quite annoying.