clients not reporting status after updating WSUS 2 to WSUS 3.0

When I upgraded to WSUS 3.0 then all my clients computers are not able to report status in WSUS. In the console, they are just being listed with yellow triangle and exclamation mark? Can anyone tell me how to fix this issue? Also when checked in the windowsupdate.log then it gave the error message as "Windows Update Client failed to detect with error 0x80244019"? Thanks for any answers.

An HTTP '404' error, suggesting that the clients are pointed to the wrong URL.

Describe to me the complete background of this WSUS server, and how it came to be a WSUS 3.0 server.

I while back I forced out WSUS 2 but the reference is not in the registry.
is it in a .net config file?
I checked the file, and clientws.DLL is ver. 2 dated 5/26/2006!
It must have been leftover.
Can I fix this, or need to uninstall,
delete 'C:\Program Files\Update Services\' and reinstall?

Thanks again.

I removed WSUS3, deleted c:\program files\update sevices ,
and deleted all clientws.DLL

clientws.DLL ver.2 was in deep subfolder of:
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\clientwebservice\21f2d155\...

clientws.DLL ver.3 was in deep subfolder of:
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\clientwebservice\48cba74c\...

I reinstalled WSUS3 successfully.

The console shows clients reporting with last date/time, but the updates show as installed/not applicable , or updates with no status. no clients show any updates needed, but they are not current. No clients show a yellow exclamation.
I tried the client fix on a few- remove susclid reg entries, restart wuau.
I think I have sufficient permissions on the server.
Anything to check on server or clients?

All appears well. Clients started reporting ater the client fix.
Thank you all contributors.