COMADMIN_E_CAT_PARTITION_IN_USE Fix (0x80110459)

You're staring at the COM+ Partition Management snap-in and trying to delete a partition. Windows throws back 0x80110459 with the message "The partition cannot be deleted because it is the default partition for one or more users." This usually happens on Windows Server 2008 R2 through Server 2022, especially after you've set up COM+ partitions for application isolation and then tried to clean up old ones.

What's actually happening here is that COM+ partitions work like isolated environments for COM+ applications. Each partition can be assigned as the default for specific user accounts or groups. When you try to delete a partition that some user or group relies on as their default, the system refuses — it doesn't want to orphan those accounts with no partition to land in.

Let's walk through the three most common causes and their fixes, from the most likely to the least.

Cause 1: A specific user account has this partition set as default

This is by far the most common scenario. You created a partition for a developer or an app pool account, made it their default, and now you want to delete it. The Component Services UI doesn't give you a straight "unassign" button on the partition itself.

The fix

1. Open Component Services — type dcomcnfg in the Run box (Win+R).
2. Navigate to Component Services → Computers → My Computer → COM+ Applications.
3. Right-click COM+ Applications and select Properties.
4. Go to the Default Partition tab. You'll see a list of users and groups, each with a partition name next to them.
5. Find the user or group that lists your target partition as their default.
6. Select that user, click Remove — or change their default partition to Global (the default system partition).
7. Click OK and try deleting the partition again.

The reason step 6 works is that removing the user from that list breaks the dependency. The partition is no longer anyone's default, so the system allows deletion. If you change the partition to Global instead, you're essentially reassigning them to a partition that can't be deleted (the global one), which also clears the block.

Cause 2: The partition is assigned to a group, not an individual user

Sometimes you'll look at the Default Partition tab and see a group like Domain Users or BUILTIN\Users mapped to your partition. The UI won't show you all members individually — just the group. You try to remove the group, but you get a similar error or the removal doesn't stick.

The fix

1. In the same Default Partition tab, select the group.
2. Click Change (not Remove).
3. From the dropdown, select Global as the new default partition.
4. Click OK.
5. Now the group's default is Global. You can go back and delete your partition.

What's tricky here is that COM+ treats groups as a single entity in that list. If you just Remove the group, the system might still hold a reference somewhere — especially if the group has multiple members who have explicitly used that partition. Changing their default to Global is safer and avoids any "object in use" remnants.

Cause 3: Corrupted or orphaned partition assignments (registry)

This one's rare but it happens, especially after a failed domain migration or when you've manually edited COM+ registry entries and left a mess. The Component Services UI shows no users assigned to the partition, but the delete still fails with 0x80110459. What's actually happening here is that underneath the hood, the partition's GUID still appears in the DefaultPartitionMapping registry key, but the UI doesn't list it because the user SID referenced there no longer exists.

The fix (advanced — back up your registry first)

1. Open Regedit as administrator.
2. Navigate to:
   

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\COM3\PartitionTable

3. Look for a subkey named with the partition's GUID (you can find the GUID in the Partition Management snap-in by right-clicking the partition → Properties → see the "ID" field).
4. Under that partition GUID, check the DefaultPartitionMapping subkey. You'll see one or more SID entries (like S-1-5-21-...).
5. If the SID doesn't correspond to any current user or group (check with wmic useraccount where sid='S-1-5-...'), delete that SID value.
6. Close Regedit and restart the COM+ System Application service (net stop COMSysApp && net start COMSysApp from an elevated command prompt).
7. Try deleting the partition again.

Be precise here — delete only the orphaned SID values, not the entire partition key. Deleting the wrong thing can break other partitions. The reason you need to restart the COM+ service is that it caches the partition mapping at startup; without a restart, the registry change won't take effect.

Quick-reference summary

If you still can't delete the partition after all three fixes, you're probably dealing with a deeper issue — maybe the partition's COM+ applications are still running. Check for that by looking under the partition in the COM+ Applications tree and making sure all applications are stopped before you retry.