error in process chain

Hi All,

          START------>INFOPACKAGE---------->DELETE INDEX------------------>DTP--------------->GENERATE INDEX  is correct without errors.

but

   if add roll up at the last after GENERATE INDEX it is throwing error

No type "Delete Index" process can be in front of process "Roll Up of Filled Aggregates/BIA Indexes" variable ZST_V6 in the chain

Message no. RSMPC011