According to the VMware vSphere Update Manager PowerCLI 5.0 Release Notes you need:
Requirements
To use Update Manager PowerCLI 5.0, you need to have installed the following software:
- .NET 2.0 Service Pack 1
- VMware vSphere PowerCLI 5.0
Update Manager PowerCLI 5.0 works only with Update Manager 5.0.
