We recently upgraded from 3.5 to 4.2.0a and I've discovered that we can't access the Documents tab. The error is:

Fatal error: return_module_language(): Failed opening required 'modules/Documents/language/en_us.lang.php' (include_path='.:/usr/local/lib/php') in /homepages/SugarCRM/SugarSuite/include/utils.php on line 694

A similar error appears when we try to edit or create email templates:

Fatal error: handlesave(): Failed opening required 'modules/Documents/Document.php' (include_path='.:/usr/local/lib/php') in /homepages/SugarCRM/SugarSuite/modules/EmailTemplates/EmailTemplateFormBase.php on line 123

I would appreciate any assistance on what I need to correct.
Tom