Always MRP is problem in the Manufacturing module of any ERP

Hmm,
Its been long time, since I worked in ERP as a full time consultant. I have worked in BaaN as a Process consultant and MIS planner (crystal reprot writer), later on, wherever I am, in whichever department or profile, I have been used for MIS, or ERP for implementation, or guidance or have been a part of selection panel for deciding which ERP we should go for the Organization I work with.
In Marmum Dairy, my senior colleague took me when he went to Marmum Dairy for two things once is, they have BaaN, another is to impelment HACCP.
Fine after a decade, I got a chance to work with the present organisation to implement the ERP. AS I faced problem in any other top end ERPs, here also the MRP givestrouble that dragged the live testing phase almost for 3 weeks.
As I have a task master or go getter ( as mentioned often by my well wishers and mentors), thisirritates, once the results are not seen from the work we put forth.