Few days back while working with list I got one problem I solved that after some goggling may be some you will help it out.
I want to create one custom column for my custom list but while creating it from list setings it was giving following error.
After some search I found that if you have created same column name with some list and if its added in site column gallery it goes there.If you delete that list all column names related with that list get deleted but it keep that column name reference in some hidden group which can not be seen through share point UI.
To solve this problem you have just execute the following script in address bar of that list page
The Script is...
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.