Error 2603

Question

Hello,

I'm having trouble in signing in to my Microsoft Office Apps even though I'm connected to the internet.

I keep having this Error 2603

Please assist

Answer 1

Are you currently using any VPN or firewall that might be blocking the connection?

Please also check your system’s date and time settings by right-clicking the date and time on the taskbar, selecting Adjust date and time, and ensuring that Set time automatically and Set time zone automatically are enabled.

Also, I recommend updating Windows to the latest version, particularly the update available at the link below: https://support.microsoft.com/topic/march-21-2026-kb5085516-os-builds-26200-8039-and-26100-8039-out-of-band-09e85404-1cb6-4ed4-9ca5-3e40d74307b9

Answer 2

Error 2603 when signing in to Microsoft 365/Office apps is typically related to connectivity or environment issues, even when general internet access appears to work.

Try these steps in order:

1. Confirm Office and Windows build

• Make sure Office is updated to the latest build.
• On Windows 10/11, also ensure Windows is fully updated, as sign-in components (AAD, WAM) depend on OS updates.

2. Test connectivity to Microsoft sign-in services

• Open Microsoft Edge (not Internet Explorer).
• Go to https://login.microsoftonline.com.
  • You should be redirected to https://www.office.com or your organization’s landing page.
• Then open a new InPrivate window in Edge and repeat the same test.
  • If either navigation fails, the issue is caused by the network environment, local firewall, or antivirus software blocking the sign-in endpoints.
  • In that case, work with the network admin to allow access and retry sign-in.

3. Check for local firewall/antivirus or proxy issues

• If a proxy is used, ensure Windows HTTP clients are configured correctly.
• From an elevated Command Prompt (Run as administrator), the admin can configure the proxy with:

    netsh winhttp set proxy <Address of proxy server>
  

• Ensure the URLs and IP ranges required for Microsoft 365 are allowed, as described in the Microsoft 365 URLs and IP addresses list.

4. Verify TLS 1.2 is enabled (older Windows)

• On Windows 8.1 or earlier, TLS 1.2 must be enabled for Microsoft 365 activation and sign-in.
• Go to Control Panel → Internet Options → Advanced.
• Under Security, ensure “TLS 1.2” is checked, then select Apply and OK, and restart the device.

5. Sign out and sign back in within Office

• Open an Office app (for example, Word).
• Select the profile name/icon at the top right.
• Choose Sign out, close all Office apps, then reopen Word.
• Select Sign in and ensure the correct Work or School account (or the account with the active Microsoft 365 subscription) is used.

6. If the issue persists

• If navigation to https://login.microsoftonline.com works in Edge and InPrivate, but Office still shows error 2603, capture the exact error details and contact your organization’s admin or Microsoft support, as deeper AAD/AADAL/WAM diagnostics may be required.

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References:

• Connection issues when signing in after updating to Office 2016 build 16.0.7967 on Windows 10
• Sign in issues when activating Microsoft 365 Apps