Except in very rare circumstances, the size of the file has nothing to do with whether you can open it or not. If   open(FILE, "bigfile") or die... is failing for you, avail yourself of "$!", which usually holds a valuable error message.   open(FILE, "bigfile") or die "bigfile: $!"; will do the trick.

Also, double-check that you have a file name "bigfile" (and not "bigfile.txt") in the same directory as the script. If you're on a Unix system, then case in the filename is significant (e.g., "bigfile" isn't the same as "Bigfile").

And please, in the future post your questions once. There might be a slight delay before your question is "approved", at which point it will be visible when you look in Newest Nodes.