Most events require the receiving partner to acknowledge receipt of that event.  Acknowledgments are either of the following:

•Positive, meaning the partner accepted the data or can honor the request.

•Negative, meaning the partner could not honor or understand the request or the data it received.

The acknowledgment requirements are listed in Events to Which a Client Must Respond and Events to Which a Server Must Respond, with the description of each event.  (See The DDE events for details.)  Likewise, each subroutine/function description in DDE Functions and Subroutines describes the response that the caller of that routine can expect based on the protocol.

Upon receipt of an event, the correct acknowledgment or required response must be carried out before another DDE exchange is initiated.  When calling a subroutine or function that transmits an event to the partner, the transmitting program should not call another subroutine or function that transmits an event to the partner until the partner has acknowledged the first event.  It is very important that any application that participates in DDE follow these rules.  Failure to do so will yield unpredictable results.