coreserver\ldlog\core.secure.log search for machine ip address or just go to the bottom of the file.
I would check the IIS permissions on the core. They may be incorrect. Check and make sure permissions on ldlogonare correct. Yeah it is Security and Patch but it has ldlogon in there also.
Also see if you can browse to HTTP://%server%/ldlogon/ldappl3.ldz from the client.
A - Please go and check that more in the detail:
1) Open IIS on the core
2) Go to Web Sites
>Default Web Site>landesk >ManagementSuite>Core-->core.secure
3) Right Click on core.secure and click on Properties
4) Click on the Directory Security tab
5) Under Authentication and access control click on Edit...
6) Make sure the the box labeled "Enable anonymous access" is NOT checked and the box labeled "integrated Windows authentication" IS checked.
7) Click Ok, Ok and close IIS
8) Open CMD and run IISRESET
B - Please check if a drive is mapped to the Core - that could also be a reason for the error message.
C - Check proxy settings on the Core - bad proxy info can cause this too.
D - Check the Proxyhost-log on the client - does it indicate any problems? We've had one cases where somehow the LIBEAY32.DLL file had been deleted on clients (C:\Program Files\LANDesk\Shared Files) and all it took was to put that back in.
LANDesk EMEA Technical Lead