redlog切换失败，这是alert_SID.log里的相关内容，请分析一下会是什么原因

打上括号的是有问题的部分
Wed Nov 26 12:17:52 2003
Thread 1 advanced to log sequence 69253
   Current log# 1 seq# 69253 mem# 0: /ems/oracle7/dbs/log1EMS.dbf
Thread 1 advanced to log sequence 69254
   Current log# 2 seq# 69254 mem# 0: /ems/oracle7/dbs/log2EMS.db
Thread 1 advanced to log sequence 69255
   Current log# 3 seq# 69255 mem# 0: /ems/oracle7/dbs/log3EMS.dbf
  
（Thread 1 cannot allocate new log, sequence 69256
  
Checkpoint not complete）
   
Current log# 3 seq# 69255 mem# 0: /ems/oracle7/dbs/log3EMS.dbf
Wed Nov 26 12:18:21 2003
Thread 1 advanced to log sequence 6925
  Current log# 1 seq# 69256 mem# 0: /ems/oracle7/dbs/log1EMS.dbf