0X80110816: Default Partition Not in Partition Set

What's actually happening here

The COM+ runtime throws 0X80110816 (COMADMIN_E_DEFAULT_PARTITION_NOT_IN_SET) when your configured default partition isn't listed in the partition set that's applied to your application or user. This error shows up most often after you've imported a partition, manually edited the registry, or switched between partition sets on a Windows Server 2008 R2 or later box — especially in environments where you're juggling multiple COM+ applications with custom partition mappings.

The core issue is a mismatch between two registry paths: the partition ID you set as default, and the list of IDs in the partition set. Windows doesn't validate this on write — it only checks at runtime. So you can save a bad config, reboot, hit the error.

Cause 1: Partition set doesn't include the default partition ID

This is the most common trigger. You set PartitionA as the default, but PartitionSet1 only contains PartitionB and PartitionC. The COM+ runtime looks at the default, checks the set, doesn't find it — error thrown.

Real-world scenario: You used the Component Services MMC snap-in to set a default partition for a specific user via the COM+ Partition property sheet, but the partition set assigned to that user's computer was left untouched. Typical after importing a partition from another server — the imported partition gets added to the computer's partition list but not to the active partition set.

How to fix it

1. Open Component Services (run comexp.msc).
2. Navigate to Component Services > Computers > My Computer > COM+ Partitions.
3. Right-click COM+ Partitions, select Properties.
4. Go to the Partition Sets tab.
5. Select the partition set that's currently active (usually the default set named "Default"). Click Properties.
6. In the Partitions in set list, check if your intended default partition is listed. If not, click Add, pick it from the list, click OK.
7. While you're there, look at the Default Partition dropdown at the bottom of that same dialog. Make sure it matches the partition you want. This is where the mismatch lives.
8. Apply, OK everything, then restart the COM+ system application or reboot the server.

After the reboot, test your COM+ application. If the error's gone, you're done. If not, move to Cause 2.

Cause 2: Corrupted or orphaned partition registry entries

Sometimes the registry entries for partitions get out of sync — a partition gets deleted but its GUID still appears in a partition set's member list, or the default partition ID references a partition that no longer exists. This happens more than you'd think after uninstalling or reimporting COM+ applications.

How to fix it

1. Open Registry Editor (regedit) as Administrator.
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\COM3\PartitionTable. This is where all partition definitions live.
3. Under PartitionTable, you'll see GUID subkeys — each one is a partition. Expand each GUID and check Name and Default values to identify your partitions.
4. Now go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\COM3\PartitionSet. This holds your partition sets. Each subkey here is a set; inside you'll find Members (a REG_MULTI_SZ list of partition GUIDs) and DefaultPartition (a REG_SZ with the default partition GUID).
5. Compare the GUID in DefaultPartition against the GUIDs listed in Members. If the default GUID isn't in Members, you've found the problem.
6. You have two options: either add the missing GUID to Members (same format, one per line), or change DefaultPartition to point to a GUID that's already in Members.
7. Export the entire PartitionTable and PartitionSet keys first — back up your work. If you mess up, you can import the reg file.
8. After editing, close regedit, restart the COM+ system application (or reboot).

Why step 6 works: The runtime reads DefaultPartition from the active partition set, then validates it against Members. If the validation fails, you get 0X80110816. You're fixing the data at the source.

Cause 3: Multiple partition sets and user assignments gone wrong

If you have multiple partition sets assigned to different users or groups, and a user's assigned set doesn't contain their default partition, this error fires. This sneaks up in Terminal Server or Remote Desktop Services environments where different users get different partition sets.

How to fix it

1. Open Component Services, go to COM+ Partitions Properties > Partition Sets.
2. Click Show Users at the bottom. You'll see a list of users and which partition set each is assigned to.
3. For each user that's hitting the error, note their assigned partition set.
4. Click Edit for that user, and in the Partition Set Assignment dialog, verify the set selected is the one you intend. If it's wrong, change it.
5. Now go to the Partition Sets tab again, select the relevant set, click Properties, and confirm the default partition is a member of that specific set.
6. Repeat for any other users. Apply, reboot.

The gotcha here: Users inherit the computer's default partition set if you don't assign one explicitly. If you've assigned a set to a user, that set's default partition must be inside its own member list — not the computer's default set. That's the nuance most people miss.

Quick-reference summary table

If none of these work, I'd check for third-party COM+ management tools that might have tweaked the registry directly — some backup/restore utilities do this and don't clean up after themselves. A last resort is to delete and recreate your partition sets from scratch, but that's heavy-handed. Try the first two fixes; they cover 95% of cases.