Microsoft recently released the version .NET Framework 4.5.
At this stage Vault 2013 (Server and Client) and all previous releases of Vault are not supported with .NET Framework 4.5. Installing .NET Framework 4.5 is done at your own risk!
Autodesk have already received reports of Vault not working properly after installing .NET Framework 4.5.
This is an extract from the Cracking the Vault, Manufacturing Community Blog