Are the devices that are giving you problems managed by CW2K/RME? Look at CW2K>RME>Administration>Inventory>Import Status and see if any of these devices had attribute errors. Are they listed under the Managed devices?
If this looks good, go to Configuration Management>Archive Status and see if any of these devices are listed under Failed, Not Supported or Partial Failure. You should also verify they are listed under Successful.
If things look good, please let us know your server OS and CW2K component and patch versions.