Not Found in User Defined Code

We were attempting to utilize a cat code field in the P0006 Business Unit program.  Our Finance Director added the code CHE to the cat code list udc table so now the two in there was blank and che.  It was then decided to not use that field but when he went in to the business unit to clear out the che and put it back to blank we are getting not found in User Defined Code error.  I can search in the drop down and I see the blank field with description '                   .' (30 characters all blank except