Columns that are very dirty with protein and do not respond to other cleaning can be cleaned with pepsin (check first that pepsin will not digest the resin - eg IgG columns - and that the column is stable at low pH). Load pepsin mixture onto the column and leave overnight. Wash off with large amounts of water. Remember that pepsin is only active at low pH (think stomach).
0.1M acetic acid
0.5M NaCl
1mg/ml pepsin