Looks like it didn't serialize?  (assuming your error is coming from the API vs the SDK)

Maybe try to pull it out, then pass it in?

$long_type = PrimType->new(10, 'long');

my $io_alloc = StorageIOAllocationInfo->new (shares => $sharesInfo, limit => $long_type );

$device->storageIOAllocation ($io_alloc);

my $virtualDeviceConfigSpec = VirtualDeviceConfigSpec->new (device => $device, operation => VirtualDeviceConfigSpecOperation->new('edit'));

my $vmConfig = VirtualMachineConfigSpec->new (deviceChange => [$virtualDeviceConfigSpec]);

$vm->ReconfigVM (spec => $vmConfig);

I'll give it a pass later to see what's going on.  Shouldn't be seeing the HASH value, should be serialized by the SDK into a proper SOAP XSD value of type 'long'.