Problems with DMA in enc28j60.c ccs stack

[Manel28]

Hi,
I am having some code's problems in enc28j60.c file. I have made a seria-ethernet converter with PIC18f25j10 + enc28j60 and ccs tcp stack. I am sending control udp packets through ethernet and another device receives the data through rs232. the device replies with a packet perfectly but after few minutes the code stops at this line of the MACCalcRxChecksum function.
while(ReadETHReg(ECON1).ECON1bits.DMAST) ;
I don't have any problem at all if I eliminate the response of the device and only the udp packets are active. It seems like DMA tries to access the RAM and stays always DMAST=1 so that the process cannot gets out the while loop. Thanls for the help

spi works at 10mbps (40MHz clock)