Adding a Description Column for a folder under Document Library

• Go to Site Actions, Site Settings
• Click Site Content Types
• Click Create
• Give the new content type a name such as "Description"
• Set the parent content type group as Folder Content Types
• Set the parent content type to Folder
• Add the new content type to a Group. I put it back in the "Folder Content Types" group
• Click OK
• Scroll down to the columns section and click Add from new site column
• Name the column and set all the usual column options
• Repeat for any additional columns
• Click OK
• Go to your document library
• Click Settings and Library Settings, or in 2010 click the Library ribbon tab and then click Library Settings
• Click Advanced and set Allow management of content types to Yes and click OK (this may already selected)
• Scroll down to Content Types and click Add from existing site content types and add your new folder content type
• Go to your document library and click the New drop down, or the New button in the 2010 Document ribbon, and add your new folder!
• Go to the View drop down and click Modify this view and add your new folder meta data columns (you will probably want to move them to just after the Name column)

The column name you have entered is already in use or reserved. Choose another name

I have faced very interesting issue last night.One of the users had changed / renamed the default content type “Title” to “Item Title” and when he tried to pull it back it gave an error – “The column name you have entered is already in use or reserved. Choose another name”

After modifying default name to custom name he realized that “Title” name had been changed to all over sites because on site all lists / libraries were inherited from parent content type. As a farm admin I even tried with no luck and got the same error.

I googled the issue and very quickly found resolution on - http://blog.weareon.net/fix-for-the-column-name-that-you-entered-is-already-in-use-or-reserved-choose-another-name/

There is a small JavaScript we have to run in browser which clears all the values in the forbidden column collection array and gives you a confirmation

And after running following JavaScript I got rid of that issue.

javascript:g_FieldName={};alert('Successfully cleared forbidden columns');