I recently happened to work on jdeveloper 10.1.3.4 and was given a task of bringing up the server. The project was using the custom libraries which the embedded oc4j was complaining that it could not find saying

Caused by: oracle.oc4j.sql.config.DataSourceConfigException: Unable to create : com.ibm.as400.access.AS400JDBCDriver
 at oracle.oc4j.sql.config.DataSourceConfigUtils.createConnectionFactory(DataSourceConfigUtils.java:283)
 at oracle.oc4j.sql.DataSourceConnectionPoolImpl.<init>(DataSourceConnectionPoolImpl.java:108)
 at oracle.oc4j.sql.spi.ResourceAdapterImpl.createDataSourceConnectionPool(ResourceAdapterImpl.java:99)
 … 13 more

This was very challenging for me because this is the first time I ran an ADF application on Jdeveloper 10g. I searched on the forum with this error and could easily find that the fix is to copy the library to

..\jdevstudio10134\j2ee\home\applib

This is just for information as this could be helpful for newbie who is still working with Jdeveloper 10g