ERROR: invalid page header in block 502758 of relation base/16388/16403

hi,

i got following error while selecting from my db

ERROR:  invalid page header in block 502758 of relation base/16388/16403

i've found some solution in this thread
http://www.mail-archive.com/pgsql-general@postgresql.org/msg101644.html

but my problem is, that there are multiple files with similar name in
the base/16388 directory.
16403 (1Gb)
16403.1 (1Gb)
16403.2 (1Gb)
16403.3 (almost 1 Gb)

so the question is, where can i find the right 502758 position (i
assume that  this is the number of 8k block position).
each file with size 1Gb has 131072 of 8k blocks.

thanx for help
fous