Is SNMP enabled on those switches? Without SNMP, LS has no way of getting any real information from them besides the header responses of the HTTP server (which I'm not sure if it even uses).
If SNMP is enabled, but you are using a community string other then public, you'll need to set the community string you use in the LS Configuration Manager. Scanning Setup -> Scanning Servers -> IP Range Scanning -> Credentials -> SNMP Community String
If SNMP is not enabled, it is rather easy to enable. For IOS, just telnet into the switch and run 'snmp-server community YOUR_COMMUNITY_NAME RO' to enable YOUR_COMMUNITY_NAME as a read only community. I don't use CatOS, but it shouldn't be that much more involved. (Don't forget to write your config)
