error in authentication - Fatal error: Class 'OAuthSignatureMethod_HMAC_SHA1' not found in .../sites/all/modules/buzzthi...

kernel drupal 6.20
Enabled modules: Buzz Post, GBuzz

I register my application on https://www.google.com/accounts/ManageDomains

Target URL path prefix: http://my_site/gbuzz/oauth

received "Consumer Key" and "Consumer Secret"
save their on http://my_site/admin/settings/buzzthis/oauth

And given Errors:

1. http://my_site/gbuzz/oauth
Fatal error: Class 'OAuthSignatureMethod_HMAC_SHA1' not found in .../my_site/sites/all/modules/buzzthis/gbuzz/gbuzz.lib.php on line 73

2. http://my_site/admin/settings/gbuzz/post
Fatal error: require_once() [function.require]: Failed opening required 'sites/all/modules/buzzthis/gbuzz_post/gbuzz_post.pages.inc' (include_path='.:/usr/share/php:/usr/share/pear') in .../my_site/includes/menu.inc on line 346

3. when creating nodes
Fatal error: Call to a member function post_activity() on a non-object in .../my_site/sites/all/modules/buzzthis/gbuzz_post/gbuzz_post.module on line 172