- Software and digital services
- Office suites
0xCAA90018
Microsoft 365 0xCAA90018 in Teams: wrong credentials
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Teams shows 0xCAA90018: you are not using the right credentials. The Windows ones you signed in with differ from your Microsoft 365 ones. Sign in again with your Microsoft 365 email and password.
Safety first
Stop and check this first
- Do not share your password with anyone claiming to be support: to check 0xCAA90018 the admin uses sign-in logs, not your password.
Safe checks you can perform
- Sign in with the Microsoft 365 account
- Correct account
- Teams client update
- Report the code to IT support
Leave these tasks to a qualified professional
- Do not attempt this professional task: Microsoft Entra sign-in logs
- Do not attempt this professional task: Teams Sign-in diagnostic
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Microsoft Entra sign-in logs
What they doThe administrator reviews the user's attempts at the time of the error in the Microsoft Entra admin center, Monitoring & health, Sign-in logs.
They must show youthe failed attempt entry.
In writingthe failure reason and the change made.
Teams Sign-in diagnostic
What they doThe Microsoft 365 administrator runs the Teams Sign-in diagnostic in the admin center with the user's email, or the Teams Sign in test in the Microsoft Remote Connectivity Analyzer.
They must show youthe test results.
In writingthe issue found and the fix applied.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Sign in with the Microsoft 365 account
- Who:
- you.
- How:
- sign out of Teams and sign in again typing your Microsoft 365 email and its password, not the Windows one if they differ.
- Result that matters:
- whether you get in with those credentials.
- If you get in:
- Teams was using the Windows account.
- If the code stays:
- check it is the right account.
- Evidence to keep:
- account used (do not write down the password).
Evidence: Why am I having trouble signing in to Microsoft Teams?
Correct account
- Who:
- you.
- How:
- confirm with your organisation which Microsoft 365 address is yours if you have several (personal, work, old).
- Result that matters:
- being sure which account Teams should use.
- If you were using another:
- sign in with the right one.
- If it was right:
- tell IT.
- Evidence to keep:
- address confirmed by your organisation.
Evidence: Why am I having trouble signing in to Microsoft Teams?
Teams client update
- Who:
- you.
- How:
- in Teams, open the Settings and more menu next to your profile picture at the top right and select Check for updates. Install anything offered and sign in again.
- Result that matters:
- whether 0xCAA90018 goes away on the latest version.
- If you get in:
- the client was missing the latest update.
- If it repeats:
- go to the next check.
- Evidence to keep:
- Teams version before and after.
Evidence: Fix Teams sign-in errors
Report the code to IT support
- Who:
- you.
- How:
- note the status code at the bottom left of the window (0xCAA90018), the time and whether other Office apps fail too, and send it to your IT admin.
- Result that matters:
- IT getting the exact code.
- If IT finds the cause in the tenant or network:
- they fix it on their side.
- If not:
- IT opens a support request with Microsoft including debug logs.
- Evidence to keep:
- screenshot of the sign-in screen with the code.
Evidence: Fix Teams sign-in errors · Why am I having trouble signing in to Microsoft Teams?
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Software and digital services
- Brand
- Microsoft 365
- Product type
- Office suites
Known code variants
- CAA90018
- Teams 0xCAA90018
What it means
Microsoft describes 0xCAA90018 as a sign-in with the wrong credentials: the Windows credentials you signed in with differ from your Microsoft 365 credentials, and Teams tries to use them. The documented action is to sign in again with the correct email and password combination and, if the code persists, contact the IT admin. The code does not say whether the account has another problem in the tenant.
Warnings and stop conditions
- Loweditorial warning
Do not share your password with anyone claiming to be support: to check 0xCAA90018 the admin uses sign-in logs, not your password.
Evidence: What are Microsoft Entra sign-in logs?
Symptoms and causes
Probable causes · in order
- Windows credentials different from Microsoft 365Common
This is the cause Microsoft gives. Confirmed if signing in with the Microsoft 365 email and password works.
Evidence: Why am I having trouble signing in to Microsoft Teams?
- Account problem only the admin can seePossible
The code persists with the right credentials.
Evidence: Why am I having trouble signing in to Microsoft Teams? · What are Microsoft Entra sign-in logs?
Virtual technician
Does 0xCAA90018 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Microsoft · 2025 · official_doc
- 2
Why am I having trouble signing in to Microsoft Teams?
Microsoft · 2026 · official_doc
- 3
What are Microsoft Entra sign-in logs?
Microsoft · 2026 · official_doc
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