Fix Next.js Build Error Module Not Found After Deploy

"Module not found" errors that only appear after deployment are among the most confusing Next.js issues. Your app works perfectly in development, builds successfully locally, but fails in production with cryptic module errors. This comprehensive guide covers every cause and provides battle-tested solutions.

This article is part of our comprehensive Deploying Next.js + Supabase to Production guide.

Why Module Errors Only Happen in Production

Development and production environments differ in critical ways:

Case Sensitivity - Production servers (Linux) are case-sensitive, Windows/Mac aren't

Path Resolution - Different module resolution algorithms

Build Optimization - Tree-shaking removes "unused" imports

Environment Variables - Missing or incorrect env vars

Dependencies - devDependencies not installed in production

Common Error Messages

## Error 1: Cannot find module Error: Cannot find module '@/components/Header'

## Error 2: Module not found…