I have nearly the same problem as kellelein, I can ping the system only some times. In debug I can see packages received, and packages put to the write buffer, but nothing happens.
I use same HW (keil evaluation board ver 3.1) and Rowley software ver. 1.7, and web demo version 4.5.0.
We like to use the FreeRTOS but it must be stable, we can’t live with a system only work some times. I don’t know about it’s the RTOS, uIP stack, the HW, but help me please.