I was trying to remove an existing column from a list through the UI without any success. The solution lay in removing it through the 'back end' with my good friend PowerShell.
Here is the code:
$web = Get-SPWeb -identity http://your/site/name
$list = $web.Lists["Your List Name"]
$column = $list.Fields["Your Column Name"]
$column.Hidden = $false
$column.ReadOnlyField = $false