Look at the permissions on your output:
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I just want to know why it is not working? It is a simple local connection. It works in my all other servers with same database.ipcs -A
IPC status from as of Wed Oct 9 14:56:32 PDT 2002
Message Queue facility inactive.
T ID KEY MODE OWNER GROUP CREATOR CGROUP NATTCH SEGSZ CPID LPID ATIME DTIME CTIME ISMATTCH
Shared Memory:
m 0 0x500004a4 --rw-r--r-- root root root root 1 68 210 210 16:53:25 16:53:25 16:53:25 1
m 6001 0xc020b8c0 --rw------- oracle dba oracle dba 7 375144448 6124 6200 11:25:45 11:26:01 16:28:144294967292
T ID KEY MODE OWNER GROUP CREATOR CGROUP NSEMS OTIME CTIME
Semaphores:
s 7536640 0xf16a3764 --ra------- oracle dba oracle dba 304 4:30:20 16:28:16
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The Oracle file should give rw to oracle and the group dba, but your output shows that it does not. Also Semaphores gives ra to oracle only, it should be oracle and dba.

Looks like a permission problem. My output looks like this:
/export/home/>ipcs -A
IPC status from as of Thu Oct 10 09:06:23 MDT 2002
T ID KEY MODE OWNER GROUP CREATOR CGROUP CBYTES QNUM QBYTES LSPID LRPID STIME RTIME CTIME
Message Queues:
T ID KEY MODE OWNER GROUP CREATOR CGROUP NATTCH SEGSZ CPID LPID ATIME DTIME CTIME I
SMATTCH
Shared Memory:
m 0 0x50005f4f --rw-r--r-- root root root root 1 4 259 259 10:52:44 10:52:44 10:52:44
0
m 101 0xa53ab7ac --rw-rw---- oracle dba oracle dba 10 160915456 461 4965 8:12:27 8:12:27 15:15:39
10

T ID KEY MODE OWNER GROUP CREATOR CGROUP NSEMS OTIME CTIME
Semaphores:
s 458752 0xe035d35c --ra-ra---- oracle dba oracle dba 104 8:19:32 15:15:40
s 720897 0x42aab180 --ra-ra---- oracle dba

I know you said you checked the file permissions, but could you check again? Check $ORACLE_HOME/dba/init.ora, ....
Actually I would go through all of $ORACLE_HOME and check the permissions on all the files. Check $ORACLE_BASE/admin/sid files also.

Good Luck -