i'm looking for a free and lightweight packetsniffer for debugging internal server errors like 500. i am using uploadify for uploading files, unfortunately there's no comfortable way to log internal errors. is there any good freeware tool for this?
you might want to take a look at http://www.wireshark.org/
Also, the Firefox Live HTTP Headers extension can be helpful in identifying issues on the http request/response cycle, without having you to take into account lower protocol layers.