chain problem

Dear all, I have two jobs using the same physical file, one job is used to send 
request (write to the physical file) and the other job is for receiving data 
queue and then updating the physical file. when i try to chain a key list to 
the file sometimes it updates correctly and sometimes it doesn't even though 
the keys are correct. I debugged the sending jobs, hold it after it's sent and 
write to the physical file, then I also debug the receiving job, and the 
receiving job would chain succesfully and update the physical file correctly. 
Could anybody please help me with this problem. Thanks Donald