Can't have more than 990 users in a group

Hello !
I'm using Joomla 1.5 and Flexiaccess.
I have to make a group (that's done) and I have to put 2,700 users in this group.
When I try to put more than 990 users and save, I'm redirected to the administrator's homepage and my changes are not saved.
Why are we limited to 990 users ? How can I turn off this limit ?

Thank you by advance

i think it your requete is too big
can you try with small number in same action ?

I added users by blocks (10 or 20 at a time) and it worked well until the number of users in this group reached 990.
After that i tried to add tiniers blocks of users at a time and I was redirected to the home of the FlexiAccess component. Then I tried to add user one by one, but the behaviour of the component didn't change : the group still have 990 users.
When adding users one by one, I tried with few users, thinking perhaps it's not the component's fault but the user's, but I had the same error.
I also tried to remove an user to the group and add another user : it worked.
I don't know what to do : I don't have any error, so I don't know where to search by now.

Thank you for the help

maybe it's a joomla limitation did you a search ?

I searched unsuccessful on Google.
If it's a Joomla! limitation, it would be very annoying, because I really need to have 2700+ users in this group...