Unique item permissions per user/group of ListItems

Question

Hello,
i have following scenario:
1.) Sharepoint group named "(Adminstrator) Company A" <-> Has Add/Edit rights on the list
2.) Sharepoint group named "Company A" <-> Has only Add/read access to the list
3.) .....many many other groups (50+) with same schema.
Each pair of groups (Company A) should "only" see their own entries in the sharepoint list.
My Logical approach and research on how to accomplish this ended up in writing a ItemEventHandler.
The problem i ran into now is that whenever i try to use "currentListItem.BreakRoleInheritance(false);" i get a access denied
message whenever the limited user group is trying to add a item to the list even when i use the SPSecurity.RunWithElevatedPrivileges(delegate().
So i wonder what is wrong. Isn't RunWithElevatedPrivileges ignoring the currentUsers rights ?
Any help would be highly appreciated.

Answer 1

Thank you all for the replies.
Meanwhile i was able to figure out myself what the problem was.
Both of your replies actually didn't solve my problem. I kept getting ACCESS_DENIED exceptions.
But the problem is that all of this happened inside of a
public override void ItemAdded(SPItemEventProperties properties)
of a SPItemEventReceiver class.
The root of the problem was that i was still trying to modify the initial "properties" object.
After i made a complete copy and re-retrieved the item from the list INSIDE of the elevatedPrivilege method i was finally able to make my desired modifications.
So for everyone who runs into this problem too:
Make sure you re-retrieve EVERYTHING(ListItem,DocumentItem etc) you want to modify with elevated privileges inside of the 
SPSecurity.RunWithElevatedPrivileges(delegate()
Thank you again,
Ralf