SD card problem

Are you running your web server on the Arduino, with html pages and images stored on the SD card? It doesn't look an easy task. You may try to verify the following conditions:

  1. Have you got enough memory on the Arduino to serve html and images? It all depends on the Arduino (is it a Mega?) and on how memory-intensive is your use of the SD library, so you should post your code if you need help with that.

  2. Is your server able to serve concurrent request from your server? When a browser reads an html containing a tag it usually sends a parallel request to the server. The Ethernet library can only handle a limited number of concurrent requests. Even managing two concurrent connections, however, may be tricky. If you suspect this is the problem you should post your code.