Thread 1 cannot allocate new log,

Dear All,
As i found some alert alternatively in  2-3-hr at my alert log.

please look the below:

 <txt>Thread 1 cannot allocate new log, sequence 4152
 </txt>
</msg>
<msg time='2013-01-16T00:34:12.291+05:30' org_id='oracle' comp_id='rdbms'
 client_id='' type='UNKNOWN' level='16'
 host_id='DB1' host_addr='' module=''
 pid='3036'>
 <txt>Checkpoint not complete
 </txt>
</msg>
<msg time='2013-01-16T00:34:12.297+05:30' org_id='oracle' comp_id='rdbms'
 client_id='' type='UNKNOWN' level='16'
 host_id='DB1' host_addr='' module=''
 pid='3036'>