IP blocked due to excessive traffic, although I'm within the stated limit

Hello,

I've lately been seeing this error page when I try to access the W3C markup validation service:

"Access to this resource is denied due to abuse from your IP address."

The message is linked to this page
http://www.w3.org/Help/abuse-info/re-reqs.html
which includes the statement "Specifically, we received at least 500 requests for the same resource (URI) from your IP address within a ten-minute time interval."

It's true that I have a homemade program that makes automated requests to the validator.  But this program always waits at least 5 seconds between successive requests, so can't possibly be making 500 or more requests in the space of 10 minutes.  The last two times (several days apart) that I've tried to run my program it has failed and, when I open the URL it tried to access in my web browser, I get the aforementioned error page.  Normal access to the validation service through my web browser sometimes works and sometimes gives the same error page.

I'd like to know why I've been blocked despite being within the limit of 500 requests in 10 minutes, and what I can do about it.

Thanks in advance,

Stewart.

Received on Thursday, 7 May 2015 12:18:26 UTC