There was the Reinhart-Rogoff error, which claimed economic growth declines (0.1%) when a nation's debt passes 90% of GDP. For years this was used to set economic policy, especially austerity measures, in western governments. When someone (a grad student IIRC) actually bothered to check the Excel formulas, an error was found and the actual number should have been a 2.2% increase instead of a 0.1% decrease.

That the error occurred isn't amazing but it is mind blowing that so much government fiscal policy was set based in part on this one spreadsheet that no one bothered to double check. Blame extends both to those who used the model to justify the policies and to those who opposed the policy but never checked the assumptions it was based upon.