Ideas on why linux OEL 5.1 server is re-booting?

One of the systems we are testing on is a quad core xeon 32 gig ram running OEL 5.1 64 bit. I have both 10.2.0.4 64 bit and 11g 64 bit. Using EMC Clariion and ASM. The ASM is running 11g and the database 10.2.0.4. It is a single instance non cluster. Fairly medium sized database 150 gig or so. When doing an rman disk backup to local internal disk (cooked file