Postmaster cannot start

Hi,

my postgresql version 7.4.5 cannot start until this morning, when i check the log file, it give me this error
this is part of my log file

DEBUG: vacuuming "pg_catalog.pg_class"
DEBUG: "pg_class": found 9823 removable, 1017 nonremovable row versions in 205 pages
DETAIL: 0 dead row versions cannot be removed yet.
Nonremovable row versions range from 148 to 196 bytes long.
There were 20 unused item pointers.
Total free space (including removable row versions) is 1477460 bytes.
183 pages are or will become empty, including 183 at the end of the table.
9 pages containing 19260 free bytes are potential move destinations.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
DEBUG: index "pg_class_oid_index" now contains 1017 row versions in 35 pages
DETAIL: 9823 index row versions were removed.
28 index pages have been deleted, 28 are currently reusable.
CPU 0.01s/0.00u sec elapsed 0.02 sec.
DEBUG: index "pg_class_relname_nsp_index" now contains 726 row versions in 197 pages
DETAIL: 6124 index row versions were removed.
126 index pages have been deleted, 126 are currently reusable.
CPU 0.00s/0.03u sec elapsed 0.18 sec.
WARNING: index "pg_class_relname_nsp_index" contains 726 row versions, but table contains 1017 row versions
HINT: Rebuild the index with REINDEX.
DEBUG: "pg_class": moved 57 row versions, truncated 205 to 20 pages
DETAIL: CPU 0.00s/0.00u sec elapsed 0.34 sec.
DEBUG: index "pg_class_oid_index" now contains 1017 row versions in 35 pages
DETAIL: 57 index row versions were removed.
28 index pages have been deleted, 28 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
ERROR: could not open segment 1 of relation "pg_class_relname_nsp_index" (target block 1183847760): No such file or directory
DEBUG: AbortCurrentTransaction
PANIC: cannot abort transaction 14135438, it was already committed
DEBUG: child process (PID 4834) was terminated by signal 6
LOG: server process (PID 4834) was terminated by signal 6
LOG: terminating any other active server processes
DEBUG: sending SIGQUIT to process 3337
DEBUG: sending SIGQUIT to process 3336
DEBUG: sending SIGQUIT to process 3335
WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT: In a moment you should be able to reconnect to the database and repeat your command.
WARNING: terminating connection because of crash of another server process
DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.

Can someone please explain to me what happen to my database, cause i not so clear,
i have a daily maintenance routine that always trigger at 4am morning.
1) will run end of day job. (every day)
2) will run vacuum full database. (every day)
3) will run analyze database. (every day)
4) will run reindex database. (every day)

saw from the log file, it's possible that server crash during vacuum process...

Question :
1) what happen to my database server? what the error meaning?
2) it is my daily maintenance routine causing that?
3) it is ok to run vacuum full every day ?
4) how can i solve this problem?

Thanks

Regards
Beh