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

Hi All,

Scenario: 

I was working for a business requirement where an "Event" has to be used and year, status are required including other fields. Furthermore The "Event" has to used in nearly 8-10 places across sites as well. Therefore I decided to design a site content type for this business requirement so that it can be used for all 8-10 sites. I created a new "Site Content Type", create a new group as "Custom Events"  as illustrated below:

Navigated to Site Actions >> Site Settings >> Site content types >> Custom Events as illustrated below

Clicked on "Events" and create a new site column "Year", column type is "Choice" Field Type and entered the choices

Created a New group named "Events"

and clicked on OK button. 

Issue: 

I bumped into an error: 

Error: The column name that you entered is already in use or reserved. Choose another name

I researched and found that this field "Year" (or Status) field belongs to the "_Hidden" group in the SharePoint Object Model MSDN and thus its not shown up SharePoint User Interface. The business doesn't want to deal with any SharePoint custom development and strictly using SharePoint out of the box features. My options were limited.

Fix: 

Step1: Navigate to the Site Actions >> Site Settings >> Site content types >> Custom Events >> Events (Content Type)

Step2: In the "Events" Content Type, from the "Add from new site column" hyperlink, "Open in new tab" option as shown below:

Step3: Type in the "Year" (which belongs to _Hidden Group)

Step4: On the browser type in following Javascript: 

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

I have to firstly run the javascript mentioned above and hit enter to get the javascript alert. 

Click the "OK" button. 

Step5: I followed the similar steps for "Status" field as well

Step5: On the browser type in following Javascript: 

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

Click the "OK" button.

A new Custom Content Type with our own Year and Status could be defined on this manner.

I hope it helps.

References:
1) SPList.Hidden property
2) Paul Galvin Blog 
3) Jack's Blog