Oracle Database Discussions

I have installed Oracle 11.2.0.3 with patch 16056266 on Linux CentOS 2.6.32-358

When I run sqlplus I get the error:
SP2-0667: Message file sp1<lang>.msb not found
SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory

I have reviewed the forums on this error and they revolve around fixing ORACLE_HOME and/or the NLS_LANG setting, but I can't see a problem with the setup here.

Oracle environment variables:
ORACLE_TERM=xterm
ORACLE_BASE=/orahome
ORACLE_HOME=/orahome/product/11.2.0/dbhome_1
ORACLE_HOSTNAME=kyora02.kymab.local
ORACLE_SID=ELN
ORA_NLS11=$ORACLE_HOME/nls/data
LANG=en_US.UTF-8
LD_LIBRARY_PATH=/orahome/product/11.2.0/dbhome_1/lib:/lib:/usr/lib

The message files are there:

ls -l $ORACLE_HOME/sqlplus/mesg
total 216
-rw-r--r-- 1 oracle oinstall 4096 Aug 5 2011 cpyus.msb
-rw-r--r-- 1 oracle oinstall 4369 Dec 4 2002 cpyus.msg
-rw-r--r-- 1 oracle oinstall 12288 Aug 5 2011 sp1us.msb
-rw-r--r-- 1 oracle oinstall 20123 Sep 29 2009 sp1us.msg
-rw-r--r-- 1 oracle oinstall 34816 Aug 5 2011 sp2us.msb
-rw-r--r-- 1 oracle oinstall 137350 Apr 19 2009 sp2us.msg

I figure this should work with the default (blank) NLS_LANG, but have tried the following without success:
export NLS_LANG=AL32UTF8
export NLS_LANG=american_america.al32utf8

Two other things that may be worth mentioning:
1. It was working fine when I completed the install, and I haven't done much since - just creating directories and copying over pfile and flash recovery area files from another system in preparation for a database clone.
None of this affected the Oracle home.
2. It isn't just sqlplus - other utilities such as lsnrctl and tnsping return similar errors.

Any ideas?