How to trace request 'Calculate Gains and Losses' process of generate NBV_LOSS code combination

  asset module :

     'Calculate Gains and Losses'  request  error ;the log show because account generateor failed to generate  NBV_LOSS   code combination;

I want to know how to trace the process of generate NBV_loss code combination (just trace request do not show abount  generate account combination info )

   very thanks for answer;