Permission denied while importing data from a file?

LS,

i'm trying to copy data into a table using a copy command using:

COPY tabelName FROM '/somewhere/somebody/datafile.txt';

I've given everybody the right to use the datafile.txt (execute, read,
write) with an incredible chmod 7777. Still i get the message:

ERROR: COPY command, running in backend with effective uid nr 666,
could not open file '/somewhere/somebody/datafile.txt' for reading.
Errno = Permission denied (13).

Why? I mean how does this happen?
Please help...

Felix