Automated Property Valuation Model with Machine Learning

Create a comprehensive Python script that integrates pandas, scikit-learn, and openpyxl to build a dynamic property valuation model. The script should load historical real estate transaction data from an Excel spreadsheet, perform feature engineering on columns like square footage, location, year built, and recent sales prices, train a predictive regression model, and generate a new Excel workbook with predicted property values and confidence intervals. Include robust error handling for missing data and implement cross-validation techniques to ensure model reliability.