You may have tax-related categories that aren't assigned to a tax form.
Quicken's Tax Schedule report shows all transactions assigned to tax forms in the Category List or assigned to transfers into and out of accounts. A category can be marked as tax related but not be assigned to a tax form. To get a report showing all tax-related transactions, subtotaled by category, run a Tax Summary report. After running the summary report, if you find transactions that should be assigned to a tax form, either recategorize the transactions or update the tax line item.
If you've purchased Quicken Home & Business, and some of your business transactions appear to be incomplete, check the Schedule C section of the Tax Schedule report for sections named Unspecified Business Expense and Unspecified Business Income. Quicken displays these sections when there are incomplete business transactions. Be sure to resolve them by tax time.