There could be many reasons why this is happening. You should make sure that you have the latest software loaded on the D2400. The software is available, free, on Quintum’s web site.
Other reasons why it may be resetting are if there are too many call requests received by the D2400 at one time.
If neither of these are the answer, you may need to contact your Quintum reseller or Quintum directly to determine the cause.