UDP checksum

Hi ,
i found a problem and i need yout kind help.
when we transfer image file over tftp most times when NET 50 is heavely loaded MD5sum check is failed.
As i have seen in ethreal all tftp packets from NET50 and to NET50 have udp checksum.
i want to know how i can be sure that udp stack on tioc side do care for udp frame checksum?
Can i debug udp stack?
With best regards