OO can not connect to DB sometimes

Environment: 

OS:Windows Server 2008 R2;  Versions:OO 9.07       Database: Oracle

OO work fine, but one day customer restart the OO central failed with the below error:  "failed to connect to OO database with error:
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor"

But after they restart the Oracle, and then restart OO, the problem solved.

This problem happened sometimes, So I do not think the configuration has problem.

What's the analysis direction?  does anyone encounter the problem before?