I have job to run trn log backup 24 X 7 every 5 min
I noticed last few days at specific point of time between 4 AM and 4:10 AM it produce same error

BackupDiskFile::RequestDurableMedia: failure on backup device '\smtrmqcrsql03cpTrnLogsAdmAdm_20020724_0405_ LOG.BAK'. Operating system error 64(error not found).

system event log shows at this time shows

{Lost Delayed-Write Data} The system was attempting to transfer file data from buffers to DeviceLanmanRedirector. The write operation failed, and only some of the data may have been written to the file.

1. Ttansaction log backup continue in next 5 min as usual
2. \smtrmqcrsql03cpTrnLogs has 24 GB of free space
3. The is no full of differential backup started or ended at the same time
4.
a) At 4:00 AM trn log size 940 kb generated
b) At 4:05 AM trn log fails
C) At 4:10 AM trn log 170 MB generated !!!!

Where to look for problem ?

Thank you

Alex