If you're using vSphere SDK for Perl 4.1 and you're connecting to anything vSphere 5 (vCenter and/or Hosts), you'll get problems.
The easiest way is to just update vCLI to 5.0 as it includes vSphere SDK for Perl bundle and this will ensure you're on the right version of the SDK to match the API. I've seen times where just updating the Perl SDK has caused some slight mis-matches. You can also just download vMA 5.0 which already includes everything, but it looks like you might be excuting this on a Windows system, so you can just install the vCLI 5.0 executable.