API version '4' for vCenter Server '<vCenterName>' is not supported.

Summary:
This helpful message appears when you attempt to use a VUM 4.1 PowerCLI cmdlet against a 4.0 vCenter / Update Manager version.
Resolution:
Uninstall VUM 4.1 PowerCLI and install VUM 4.0U1 PowerCLI.
Takeaway:
Read the release notes and hope that VMWare has right download link posted on their site, which as of this posting is wrong.  The link posted above is correct.