How to delete big amount of users with one click in admincp?

[ka81]

Hello.
Admincp - Users - Prune / Move Users (forum/admincp/user.php?do=prune)
I choose:
All usergroups
Has not logged on for 2000 days
Join Date is Before 20 april 2008
Posts is less than 1

find. It shows me result with 25000 users, that I want to delete.
I click on Delete and it shows me message: first - Invalid action specified , after that - No Users Matched Your Query.
If I choose onlt 50-100 from that result-list I will succed with deleting. So there are somewhere some limitation for users amount to be deleted at once. Where is that? How to change it at least to 2000?