I'm almost certain that there can be a limit on the amount of data that a web server - or at least, Apache - will accept via POST. The reason being that otherwise there's a simple denial-of-service attack possible, by just throwing loads of data at the server.

(/me rummages around in the docs)

If you're using Apache, the LimitRequestBody directive could be very relevant.

I think CGI.pm has a similar option. (sfx: more rummaging noises)

Aha! CGI.pm: Avoiding denial of service attacks You may need to set (or change) $CGI::POST_MAX.

What I'd do first, if I were you, would be to check whether or not the data is actually being received in full. I.e. as soon as at arrives, dump it out to the error log.

If none of the above is any help then post details of your web server, and some code if appropriate, and maybe there'll be other things to try.

hth,
andy.