[otrs] answering to ticket is slow

Hi, When I try to answer a ticket (eg. empty answer) is takes a long time before composing screen appears. When I first installed otrs, it was ok and worked fine. Then suddenly it started to act slow. There are about 4000-5000 tickets in database, if it matters. Server is fast enough and OS is debian. Otrs version is 1.3.1. It was slow in previous version also. All other actions works fine. Any ideas? Thanks, Toni Maatta