The Title column comes default on any list you are going to create in SharePoint, it's also by default a Single line of text type. This introduces problems if you don't want a Title column or if you want that Title column to be another column type.
Hidding the Title column solves your issue if you just don't want a Title column. But if you try to create a new column named Title with a different column type, you'll get an error that Title still exists.
Follow these steps to remove or change the Title column:
1. Go to Settings > List Settings > Advanced Settings on the list.
2. Click YES radio button to allow management of content types and hit OK.
3. You will now see the Item content type under Content Types, click Item.
4. Click on the Title column.
5. Select the radio button Hidden under Column settings option to make Title hidden and click OK.
6. If you want to make a new Title column with a different column type, click Title again and then click Edit column in new window. In that new window change Title to anything else, make sure Require that this column... is set to NO and hit OK. Close the new window and click OK on your main window.
7. You will now see Title is no longer there when you click New.
8. You can now create a new column, name it Title and give it any column type you want.