JTS/JTA Transaction Aborted Exception

[G Mike]

We are having a WCS Store running in WCS5.1.1 version, we are getting this exception frequently in our wcs.log, when we stop and start the server this is not happening for few days, after that the freq. of this exception is keep on increasing, we are having a max. connection pool of 30 and heap size as 198m, and oracle as database.
com.ibm.ejs.cm.exception.TransactionAbortedException: JTS/JTA transaction has been aborted
at java.lang.Throwable.fillInStackTrace(Native Method)
at java.lang.Throwable.fillInStackTrace(Compiled Code)
at java.lang.Throwable.<init>(Compiled Code)
at java.lang.Exception.<init>(Compiled Code)
at java.sql.SQLException.<init>(Compiled Code)
at com.ibm.ejs.cm.portability.PortableSQLException.<init>(Compiled Code)
at com.ibm.ejs.cm.exception.TransactionAbortedException.<init>(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectO.enlist(Compiled Code)
at com.ibm.ejs.cm.pool.OnePhaseConnectO.enlist(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectO.allocate(Compiled Code)
at com.ibm.ejs.cm.pool.OnePhaseConnectO.allocate(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectionPool.allocateConnForTransaction(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectionPool.findConnectionForTx(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectionPool.allocateConnection(Compiled Code)
at com.ibm.ejs.cm.pool.ConnectionPool.getConnection(Compiled Code)
at com.ibm.ejs.cm.DataSourceImpl.getConnection(Compiled Code)
at com.ibm.commerce.base.helpers.BaseJDBCHelper.makeConnection(Compiled Code)