[Zope] CONFLICT Competing writes?

Hi, I used a dtml method called run_program_action to process user form input, using the POST method and ENCTYPE="multipart/form-data". When I tried to submit simutaneously from two browser window, I got this error message from the Z Server console: 1999-11-24T06:43:40 INFO(0) Z2 CONFLICT Competing writes at, /Stat/rserver/simu01/run_program_action ----- form ----- {} Where the line below -- form -- should display my form input. But in the two submissions only one got the desired resonse, the other responded erroneously because the form input was lost due to CONFLICT. I heard that Zope is multi-threaded. Why can't it start two instances of the same DTML method? How can I solve this conflict problem?