From VmWare Blog, an important KB article for those upgrading from VMware View 4.0.x
Those of you using VMware View have probably already seen this post about the potential of data loss if you do not follow the specific instructions in the KB article when upgrading from View 4.x
We have another equally important piece of information you also want to be fully aware of.Customers that are upgrading their vSphere environment to 5.0 need to understand that VMware View 4.x is not supported in vSphere 5.0. View 5.0 is however, backwards compatible to several older versions of vSphere. It is then necessary to upgrade your View infrastructure first, before vSphere.
Please consult KB vSphere 5.x does not support View Manager 4.x (2006216) for details on this matter.