OM keeps failing with Process : OpManagerProcess [ FAILED ]

Hello, support.

I am evaluating the OM running on a Linux server. I use a dedicated mysql server. After the installation, everytime I started OM it gets this error. I deleted all the OM tables, then started up again. the error just won't go away.
I can't scan my networks for snmp-enabled devices. It just did not discover any device. If I tried adding a device manually, it said it's not reachable even though the device is pingable from the OM server. I turned off the host FW on the OM as well. I had another OM installed using the default embedded mysql. that OM is able to scan the network.
Please help.
Thank you,

Starting AdventNet WebNMS "Primary" Server Modules, please wait
Process : OpManagerProcess               [ FAILED ]

Product = OpManager Version x.x
          Service Pack Version =NONE
          os name=Linux
          os version=2.6.32-279.11.1.el6.x86_64
          os architecture=amd64
          java version=1.5.0_11
          java vendor=Sun Microsystems Inc.
          java specification=Java Platform API Specification
          java specification version=1.5
          java vm name=Java HotSpot(TM) 64-Bit Server VM
          java vm information =mixed mode
          java compiler=null