Fixing ERROR_TOO_MANY_SIDS (0x0000056D) on Windows

What's actually happening here

The error 0x0000056D — ERROR_TOO_MANY_SIDS shows up when Windows tries to create an access token for a user or process and runs into the hard limit of 1,024 SIDs per token. That's not a soft limit you can tweak in the registry; it's baked into the kernel's security reference monitor.

You'll see this error most often in domain environments with lots of nested groups — think Active Directory with dozens of universal groups, domain local groups, and global groups all stacked on each other. The token accumulates SIDs from every group the user belongs to, including nested memberships. Once you cross 1,024, the API calls like CreateProcessAsUser, LogonUser, or even OpenThreadToken fail with this code.

I've seen this happen on Windows Server 2016 and 2019 with users in 40+ groups that each contain 30+ nested groups. The token grows like a balloon. The fix isn't complicated, but it does require understanding where the bloat comes from.

Cause #1: Too many direct and nested group memberships in Active Directory

This is by far the most common cause. A user's token includes SIDs for every group they're a direct member of, plus every group that's nested inside those groups. If you have deep nesting — say Group A contains Group B, which contains Group C — the user gets SIDs for all three.

To check if this is your problem, run this PowerShell command on a domain controller to see the user's token SID count:

$user = Get-ADUser -Identity "username" -Properties memberOf
$tokenGroups = [System.DirectoryServices.AccountManagement.UserPrincipal]::FindByIdentity(
    [System.DirectoryServices.AccountManagement.PrincipalContext]::new('Domain'),
    'SamAccountName',
    'username'
).GetAuthorizationGroups()
$tokenGroups.Count

If the count is over 1,000, you're close to the edge. Over 1,024 and you'll hit the error.

The fix: Reduce group memberships. Don't just delete groups randomly — audit which ones are actually used for access control. Use Get-ADGroupMember to find groups with hundreds of members and consider replacing them with group nesting that flattens the hierarchy. For example, instead of nesting Group A → B → C, put the user directly in Group C if that's the only one granting permissions.

A more aggressive approach: use security groups with scope set to Universal only when necessary. Domain local groups can also add bloat because they include SIDs from trusted domains. If you don't need cross-domain access, stick to Global groups.

Cause #2: Excessive local group memberships on the target machine

This one's trickier because it's not about AD — it's about the local machine's group membership. Every local group the user is a member of adds SIDs to the token too. If you've added a user to dozens of local groups (like Users, Backup Operators, Performance Log Users, etc.), that stacks up fast.

The trigger: A user who's in 50 AD groups and 20 local groups on a server could easily cross 1,024 total SIDs after nesting.

The fix: Open lusrmgr.msc on the affected machine and check the user's member of list. Remove them from any local groups they don't actually need. For servers, avoid adding users to Administrators unless absolutely required — that group alone can add SIDs from every subgroup it contains on some builds.

You can also use whoami /groups from a command prompt to see the full SID list for the current user. Pipe it to a text file and count lines:

whoami /groups > groups.txt
# Count lines in the file, subtract header rows

Cause #3: Kerberos token size limits (less common but real)

This is a different limit, but it can manifest as the same error in certain scenarios. Kerberos tickets have a size limit of 65,535 bytes for the PAC (Privilege Attribute Certificate). If the group SIDs alone exceed that, the Kerberos authentication fails, and the system falls back to NTLM — which doesn't have the same SID limit. But if you're using LogonUser with LOGON32_LOGON_NEW_CREDENTIALS or similar, the NTLM token still gets the same 1,024 SID cap.

The fix here is the same as Cause #1: reduce group memberships. There's no registry key to increase the token SID limit. Microsoft's documentation is clear: the limit is hardcoded in the TOKEN structure at ntdef.h.

One workaround that sometimes helps: use filtered attribute sets in AD to exclude certain SIDs from the token. This requires modifying the ms-DS-Group-Auto-Remove attribute on the user object, but it's risky — you can accidentally block access to resources. I don't recommend it unless you really know what you're doing.

Quick-reference summary table

The bottom line: you can't push past 1,024 SIDs per token. Don't waste time looking for a registry hack — it doesn't exist. Clean up group memberships, and if that's not possible, restructure your AD groups to be flatter. The error will disappear once the count drops below the limit.