要先確定Server和Client端電腦是在同一個網域下，如果不是的話就沒辦法安裝agent。
不然就要先升級到SCE SP1，這樣就能支援workgroup下的電腦管理了。

以下是微軟建議的檢查步驟，可以檢查出RPC是否被Firewall擋掉。

For the RPC server is not avaviable problem:

1. Restart RPC service on and ensure 'Remote Registry' service is start on problematic client.
2. On the problematic server, check if DCOM was disabled. Enabled DCOM by going to DCOMCNFG - My COmputers - Right CLick - Default properties- Enable DCOM on this computer

1). Log on to the SCE server with the domain\administrator account
2). Start – run – wbemtest.exe
3). Click on Connect
4). In the Namespace box, enter \\<computername>\root\cimv2 and click on Connect, where the computername here is the target problematic computer’s name.
5). Click on Query
6). In the query box, enter "Select * from Win32_OperatingSystem" (without quotation) and click on Apply.
Does any error prompt?
4. Make sure that RPC traffic is open on the firewall between the SCE server and the client. For example, if you have a ISA firewall, make sure the RPC filter is disabled.
5. Run Nslookup command and ensure the affected computers FQDN can be resolved properly.
6. Then, Reboot SCE server.

此外,WSUSSSLCert.cer 是放在Essentials 2007 Management Server的<Essentials 2007 folder>\Certificates目錄下, 你要將它copy到用戶端電腦的<agent installation folder>\Certificates目錄下