the collision is probably because the switch is delivering the data faster than your Ethernet processor can handle the datarate is my guess, if the buffer overflows or the overhead is too large for the current transport, collisions happen.

Yea, the link is 10Mbps, but that doesnt mean the rest of the hardware can buffer, process, and handle the data stream at that exact rate. A good example of this is the arduino, and the wiznet ethernet controller. its stable at 100Mbps, but that doesnt mean the processor can handle 100mbps data rate.