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

When you’re creating columns either the Site Columns or the List Columns in SharePoint, it might show a message stating

“The column name that you entered is already in use or reserved. Choose another name.”.

Ideally, If it is reserved column name then you should avoid giving that name.

Still there are cases when you have to change the name.....

Here is the fix for this issue.

Just check all the columns in the list.Any column with the same name(both display name and internal name)? - No. Then that must be reserved name.

FIX :

There is a javascript array variable which had all collection of forbidden column names. Clear this array and then try creating the column.

To clear the columns the following script should be entered in the address bar of the browser and hit enter.

javascript:g_FieldName={};alert('Successfully cleared column Names');

The above script clears all the values in the forbidden column collection array and gives you a confirmation. Now try creating the column now.You should be able to.