It's due to the Safedisk 2.8 protection as I believe DF3946.TMP is a safedisk file.
There are instructions on backing up SD 2.8 using Diskdump and Burn-at-once, search the forum and you'll find it straight away.
Or you could get the new Alcohol 120% which is capable of backing up Safedisk 2.8.
Also, ur burner may not be up to the job. Have a look at the supported writers page at
www.elby.ch and check to see if your burner has two sheep in the EFM coding column.