I get following error in my alrt.log file

Errors in file f:\oracle\proddb\8.1.6/admin/bdump\prodLGWR.TRC:
ORA-00345: redo log write error block 4211 count 1
ORA-00312: online log 1 thread 1: 'F:\ORACLE\PRODDATA\LOG01A.DBF'
ORA-27072: skgfdisp: I/O error
OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 33) The process cannot access the file because
another process has locked a portion of the file.

Thu May 17 10:10:00 2001
Errors in file f:\oracle\proddb\8.1.6/admin/bdump\prodLGWR.TRC:
ORA-00346: log member marked as STALE
ORA-00312: online log 1 thread 1: 'F:\ORACLE\PRODDATA\LOG01A.DBF'


What these means? and How to correct? Please help me.