System is not responding when doing post

Dear all, One of our client DB size is 80 GB,recently upgraded to Nav 2009 and its not DB in SQL. When ever doing any posting sytem is going to not responding state. If we go to do task manager then end task it, and if I open the data base I can see that posting is completed.what might be the problem.can any one suggest for this problem.

I assume they tested posting in the upgraded system before going live with it? In that case there was probably something that happened during the code merge process.