ATP Processing error while processing RLM schedules

Hello,

We were unable to process the RLM schedules as we are getting ATP error

ERROR
-----------------------
Message Found ==> Scheduling failed.

Try ATP again later
get message context
schedule line ==> 19279889
ProcessOrderAPI Error ==> Scheduling failed.

Try ATP again later



Problem Description
---------------------------------------------------
Error :: The Process Order API returned the following error for Item 4089467 and request date 2013/12/02 00:00:00 :
Scheduling failed.

due to this demand could not be processed on time,the error is going away when schedules are submitetd after a few hours,even within a schedule, the processing fails for some items only.

Please suggest.

Thanks