Because when DBA add datafiles,  the datafile name with the end "space"  For example:   'a ' !='a',
the dbua check the datafiles trim the space, but when alter database datafile '        'autoextend on ;
report the datafile not found,.
need take action as below:
1.Find the data file  which name have space                                                                                        
 select file_name, length(file_name), length(trim(file_name)) from dba_data_files where length(file_name)!=length(trim(file_name));
                                                                                                                                   
2.Rename the data file name which have hide space                                                                                  
 sqlplus >startup mount                                                                                                            
 ! mv "/u11/oradata/mdw/lss1_p12_11.dbf " /u11/oradata/mdw/lss1_p12_11.dbf                                                         
 ! mv "/u13/oradata/mdw/lss1_p12_13.dbf " /u13/oradata/mdw/lss1_p12_13.dbf                                                         
 ! mv "/u14/oradata/mdw/lss1_p12_14.dbf " /u14/oradata/mdw/lss1_p12_14.dbf                                                         
                                                                                                                                   
alter database rename file '/u11/oradata/mdw/lss1_p12_11.dbf ' to '/u11/oradata/mdw/lss1_p12_11.dbf';                              
alter database rename file '/u13/oradata/mdw/lss1_p12_13.dbf ' to '/u13/oradata/mdw/lss1_p12_13.dbf';                              
alter database rename file '/u14/oradata/mdw/lss1_p12_14.dbf ' to '/u14/oradata/mdw/lss1_p12_14.dbf';                              

conclusion: this one oracle small bug.