I get pretty much the same over here...
I get this for eg when i try to download the 'Mobile' v0.3 by 'ChuckRoast' in the list of available templates:
Code:
Fatal error: Cannot instantiate non-existent class: archive_tar in [pligg directory]/modules/template_management/template_management_main.php on line 233
Of course i have Pligg version 9.9