oracle.ias.cache.CacheException: java.io.FileNotFoundException: /javacache.log (Permission Denied)

After applying ATG_PF.H RUP4(patch 4676589) or TXK Rollup P (patch 5759055), you'll see a new error logged in $IAS_ORACLE_HOME/Apache/Jserv/logs/jvm/XmlSvcsGrp.###.stderr file:
oracle.ias.cache.CacheException: java.io.FileNotFoundException: /javacache.log (Permission Denied)

The cause is described in metalink note 397744.1 :

Since the value of $APPLRGF was not passed to the jvm at startup via a wrapper.bin parameter the directory being defaulted for javacache.log is going to "/" ( root ), which should be correctly unwritable by the Apache/Jserv process.

The simple fix to this error is to apply TXK AutoConfig Rollup Patch Q (Jul/Aug 2007, Patch 5985992). If you are not in a position to do so right now, you can follow the manual steps of modifying the autoconfig templates which is described step by step in note 397744.1