We have had this support question and thought we would post the answer to help anyone else who encounters the same problem.

Problem detail
When running BurnInTest for a long period with the disk test active, the following errors are reported, seemingly at random.

Test file could not be created. Check access privileges
Test file could not be re-opened.
Access is denied. (5)
Disk, Write block - File name: C:\BurnInTest test files\~bittestC00xxx

Solution 1 - AV software

When testing a formatted hard drive, BurnInTest uses creates, writes and reads a number of test files from the hard drive. These files have names like,
C:\BurnInTest test files\~bittestC00001
Some anti-virus solutions seem to open the test files in the background and keep the file locked for an extended period of time. As the file is locked, it can't be opened nor read back from the disk, resulting in the above errors.

The solution is to disable the anti-virus software while testing, or at least exclude the folder from being scanned by the AV software.

The kind of behaviour by anti-virus software is also likely to cause problem in real software.

Solution 2 - DiskKeeper
Similar behaviour was also observed with Condusiv's Diskkeeper software running in the background. Diskkeeper claims faster speeds and less crashes, but in reality it is locking file (presumably to de-fragment them) which then causes other applications to error out. We strongly suggest you disable or uninstall the DiskKeeper.