0 Can’t mount Public Folders

Had an error demoting an old Exchange 2003 after a swing migration to Exchange 2010.
There was no way I could remove it.
After some stumbling around registry, I removed it,but...

In the end, Exchange 2010 server couldn’t mount Public Folder database store.

Found this solution on some forum. (Sorry don't remember particular where.)

Run adsiedit.msc

Then :
Configuration-Configuration-Services-Microsoft Exchange-Orgname-Administrative Groups-Exchange Administrative Group

‘Folder Hierarchies’ folder – recreate it:

Create “Folder Hierarchies” under the Exchange Administrative Group

1. Right click on Exchange Administrative Group

2. Select New Object

3. Select msExchPublicFolderTreeContainer for the class and click Next

4. Enter the following for the value: Folder Hierarchies, click Next

5. Click Finish
Create Public Folder Tree Object

1. Right click CN=Folder Hierarchies -> New Object

2. Selected msExchPFTree for the class

3. For the value we entered, “Public Folders” and clicked next

4. Clicked on the “More Attributes” button, selected msExchPFTreeType and set the value to 1. Note: This is very important that this value is set to a value of 1 as this tells Exchange that this is a MAPI Tree

5. Click Ok and then finish
Populate msExchOwningPFTreeBL attribute object of the PF Stores in the organization

(Since this attribute is not directly editable, you have to follow the below steps to do this for each PF store)

1. Get properties of the newly created “Public Folders” Tree object in ADSIEdit.

2. Copy the distinguishedname value to the clipboard and then click cancel.

3. Navigate to the Storage group that contains the Public Folder Store for this server and get properties of the public folder database object in the folder.

4. Locate the msExchOwningPFTree attribute and paste in the value that was copied to the clipboard in step 2. Click OK.

5. Restart the Information Store Service

6. Now try to mount the PF store and see if we can access it fine now.
Soon as the Information Store service was restarted it came online.