You may get errors on items that are already in your company. For example, the "Hours" and "Services" items that are created by default. The best thing to do is not to import these items. The rest of your items should still get imported.
If importing Products/Services, cancel the import, make sure that those accounts exist, and then try again. To avoid this error, either import your Chart of Accounts first before your Products and Services list. Or if you have just one or two missing accounts, you may want to create them manually after the import.