The host returns esxupdate error code:15

I keep getting this error on patching some esxi 5.0 hosts

Remediate entity

10.50.233.67

The host returns esxupdate error code:15. The package manager transaction is not successful. Check the

Update Manager log files and esxupdate log files for more details.

5/22/2013 4:32:31 PM

5/22/2013 4:32:31 PM

5/22/2013 4:55:51 PM

any idea why?