You need to view the sweeper logs.
ALSO SEE: How do I view the log files?
The sweeper log will point you to the problem.
Example 1:
[2005-10-24 08:55:28] Version [1.5.0.0]Error Opening Archive 3 Times :36_07D5F640BCBA.zlb:The archive file appears to be corrupted
[2005-10-24 08:55:29] Version [1.5.0.0]Error : no call info for recording :/opt/amethyst/data/work/36_07D5F640BCBA.zlb
The log entry "36_07D5F640BCBA.zlb", 36 referes to the IP of the USBClient,
that there is a problem with, please check the "USBClient.log" on that PC.
Under investigation!