oracle 10g 出现em登陆，服务器不可用的错误(windows下)

java.lang.Exception: Exception in sending Request :: null这样的错误

在Oracle论坛上查到了解决办法:
http://forums.oracle.com/forums/thread.jspa?threadID=320574&tstart=0&messageID=1374397
go to your emd.properties file and change agentTZRegion parameter
In our case it was: agentTZregion=Australia/Sydney.

Reboot and watch dbconsole work.

Cause of OEM Database control/agent (single DB) problems:
I have found out that for my single instance configuration (no grid agents), the common cause of
"Agent process exited abnormally during initialization" in system event log,
"java.lang.Exception: Exception in sending Request :: null" in OEM Database Control Database Instance home page
"status pending" in OEM Database Control Database Instance home page
"Io exception: Unknown host specified" in OEM Database Control Database Login
was an incorrect time zone autoconfigured by the Database Control service.

The solution is
1. Kill the java process which is the console portion of OracleDBConsole<SID>
2. Edit the emd.properties file to have the correct timezone
3. Reboot or restart the OracleDBConsole<SID>