BalaReva.Excel.Activities

Hi,
when we try to launch Robot on the process from Orchestrator that uses “Delete Sheet”, we have this error:

workflow: UiPath.Core.Activities : Cannot create unknown type ‘{clr- namespace:BalaReva.Excel.Sheets;assembly=BalaReva.Excel}DeleteSheet’

when the process runs from UiPath Studio works fine

Could we miss some configuration on Orchestrator or Orchestrator machine that is different from robot machine?
Note that the robot run on the same machine where we test the process with Studio

thank you
Guido