Try what el_loco sugested,
Mobile applications are generaly not stable (for now). Although the new Smartphones are smart, they have turned into micro computers.
Like when your computer crashes..same thing can happen to the new smartphones.
Also when you install more software on a PC, a few more seconds take it to start up. This is because it is running all the software that is set to run in registration (startup).
Samething probably goes to the smartphone.
Other then that, if you get rid of those applications, and it keeps happening..thats an issue for the Nokia Service Center.
The N91 is a very new mobile. It could have bugs/issues with firmware ect.
By the way,
..its an awsome phone!
Good Luck,
Tal
I own a 5210, 5140 and now..the new 3250. Symbian 60 Series OS 3.0 ..just the best.