SID Overflow on Logon: Fix ERROR_TOO_MANY_CONTEXT_IDS (0X00000568)

What's actually happening here

You're staring at a logon failure on a Windows machine—Server 2016, maybe a domain-joined workstation—and the event log spits back ERROR_TOO_MANY_CONTEXT_IDS (0X00000568). Translation: the user’s security token hit the hard limit of SIDs (security identifiers) it can carry. That token gets built every time someone logs in, combining the user’s own SID plus every group they're a member of. In big, nested AD environments, that count climbs fast. I had a client last month—a hospital with 20 years of accumulated groups—where one account was in 1,200+ groups. Instant token bomb.

The default limit on the security token is about 1,024 SIDs (though the actual number depends on token version and OS). Hit that ceiling, and Windows refuses the logon outright. No negotiation.

Cause #1: Excessive group nesting in Active Directory

This is the big one. Most people see “too many SIDs” and think it’s a registry tweak. Nine times out of ten, it’s just that someone nested groups too deep or threw a user into too many groups. AD doesn’t warn you when a user’s effective group membership (including nested group expansions) crosses the token limit.

How to check

1. On a domain controller, run gpresult /user username /scope user /v—but that only shows applied GPOs, not total SID count. Better: use PowerShell with the Active Directory module:

Get-ADUser username -Properties memberOf | Select-Object -ExpandProperty memberOf | Measure-Object

That gives you the count of direct group memberships. But the real count includes every nested group. So pull the expanded list with:

Get-ADGroupMember -Identity "Domain Users" -Recursive | Where-Object {$_.objectClass -eq 'group'} | Measure-Object

If that count is north of 900, you're in the danger zone. The total token count includes the user SID, computer SID, domain SID, plus any well-known groups (Everyone, Authenticated Users, etc.). So actual group expansions should stay under 900 to be safe.

The fix: flatten group memberships

You need to reduce how many groups the user is effectively in. Two approaches:

• Remove the user from unnecessary groups. Audit membership—most people accumulate groups they don't even need.
• Flatten nested groups. If you have Group A that contains Group B that contains Group C, each level triples the SID count for users at the bottom. Restructure so users are direct members of the groups they need, not nested several layers deep.

This isn't a quick registry fix—it's an AD hygiene issue. But it’s the only real solution for most cases.

Cause #2: The token size limit is too low for normal usage

Sometimes the group count isn't crazy, but the OS token size setting is too conservative. By default, Windows sets the security token maximum size to 12 KB (0x3000 bytes) on pre-Win10/Server2016 systems. Newer OS versions bumped it to 48 KB. Each SID averages about 40 bytes, so 12 KB gives you around 300 SIDs. That's tight.

If you're on an older OS (Server 2008 R2, Windows 7) and have a reasonable 400 groups, you'll hit the limit.

How to check your current token size

Open Registry Editor and go to:

HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters

Look for MaxTokenSize (DWORD). If it's missing or less than 48000 (decimal), that's your bottleneck.

The fix: bump MaxTokenSize

1. Navigate to HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters. If the key doesn't exist, create it.
2. Create a DWORD named MaxTokenSize and set it to 65535 (decimal). That's the max allowed—leave it there if you want headroom.
3. Reboot the machine.

This gives the token room to breathe. But don't set it higher than 65535—Windows won't accept it, and you'll break things. I've seen people try to go to 99999; don't. Stick to 65535.

One caveat: this only applies to Kerberos tokens. If you're using NTLM (no domain, or older setups), this won't help. NTLM has its own limit, but that's a different error.

Cause #3: Security software or third-party filters interfering

This one's sneaky. Sometimes the token itself is fine, but an antivirus or security product (I'm looking at you, McAfee with Access Protection, or certain endpoint detection tools) intercepts the logon process and adds extra SIDs or security descriptors to the token. I had a client running a health-care application that injected SIDs for role-based access. That tipped the total over the edge.

How to diagnose

Boot the machine in Safe Mode with Networking. Try logging in with the same user account. If the error disappears, a third-party service or driver is the culprit.

Also check the System event log for entries from source Microsoft-Windows-Security-Kerberos or LsaSrv—they might hint at which component added extra SIDs.

The fix: disable or reconfigure the offending software

• Short-term: disable the security software's logon injection feature. For McAfee, that's often the “Access Protection” rule that adds SIDs to tokens. In Symantec Endpoint Protection, look for “token augmentation” settings.
• Long-term: update the software to a version that respects the token size limit, or reconfigure it to not add unnecessary SIDs.

If you can't identify the third-party software, do a clean boot: run msconfig, disable all non-Microsoft services, restart, and test. Then re-enable services one by one until the error returns. That isolates the offender.

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