Sign-in & Login Problems

How to Fix OneDrive Sign-In Error: Prototype Undefined or Null

Maira Mehtab Sep 27, 2026 869 views

Question details

Users are encountering a script error preventing Microsoft account authentication when attempting to sign in to OneDrive.

Product: Microsoft OneDrive
Device & OS: Windows
Scenario: Attempting to sign in to a Microsoft account on the desktop application after a previous sign-out.
Observed behavior: The application displays a script error stating 'Unable to get property Prototype of undefined or null reference', which blocks the sign-in process.

Before you start

Ensure you have your Microsoft account credentials ready and verify that your Windows operating system is fully updated before troubleshooting the OneDrive application.

Solution 1Recommended

Reset the OneDrive Application

Resetting OneDrive clears its current configuration state and often resolves sync and sign-in script errors without risking data loss.

This process will restart the sync engine and rebuild the application's cache, which is a common fix for undefined script errors during authentication.

Open the Run dialog

Press the Windows key + R on your keyboard to open the Run command window.

Execute the reset command

Type %localappdata%\Microsoft\OneDrive\onedrive.exe /reset and press Enter.

Wait for OneDrive to restart

The OneDrive cloud icon in your system tray will disappear and then reappear. If it does not reappear after a few minutes, open the Start menu, search for OneDrive, and launch it manually.

Data Safety: Resetting OneDrive will not delete your local files or folders. It only resets the application settings and initiates a fresh sync.

Solution 2

Uninstall and Reinstall OneDrive

If resetting does not resolve the script error, reinstalling provides a fresh, uncorrupted version of the application.

Solution 3

Perform a Clean Boot and Test a New User Account

Use this method to determine if a third-party software conflict or a corrupted Windows user profile is causing the authentication script error.

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Frequently Asked Questions

What causes the 'Prototype of undefined' script error in OneDrive?

This script error typically occurs when the cached login scripts used by the built-in Windows browser components become corrupted, or when third-party applications interfere with the Microsoft account authentication window.

Will I lose my files if I reset or reinstall OneDrive?

No. Your files remain safely stored locally on your hard drive and in the cloud. Resetting or reinstalling the app only resets the software's settings and triggers a fresh synchronization process.

Why does OneDrive use a script for sign-in?

OneDrive relies on built-in Windows web components (like Edge or Internet Explorer core) to securely render the Microsoft account authentication window. If these web components encounter an issue or have corrupted cache, script errors can appear.

Login & Account Issues