Discovery task. Systems not added with status 53

Hello,

I have a customer that is running IP range discovery in their environment.

Some of the hosts are discovered right, but others don't. In the logs the systems that have some issues being discovered show the following:

03/26/2013 11:22:35:2:4000: Discover:  SysDscComplete for [190 - 144.178.116.225] with a status of 53.

I have checked on the documentation for status 53 but have not found anything.

Any ideas?

Thanks!