Thie following warning message is seen when a file is in use and therefore being handled by VSS (since VSS creates the GLOBALROOT snapshot path):
Warning: 21:48:35 Unable to open file: C:\Program Files\Computers\Diagnostics\
Program Files\Computers\Diagnosticss\Diagnostics\ ServiceHost_20100620192402.xml
(The system cannot find the file specified)
When you see this error, the problem is typically with VSS. It often indicates that the snapshot of the specified file is not available, as VSS will have overwritten it if there was insufficient space.
Increase the volume shadow copy area, as described here.
The cause may also be another VSS error, so check the event logs for volsnap or Volume Shadow Copy errors.