Thisis a by default behavior in LDAP query. To understand this issue, first we should know what is MaxPageSize.
MaxPageSize - This value controls the maximum number of objects that are returned in a single search result, independent of how large each returned object is.
By default MaxPageSize is 1000. So when you perform a search where the result might exceed this number of objects the error “might exceed this number of objects” will appear. To correct this behavior we have to options.
First, Microsoft recommend that we must specify the paged search control. This is to group the returned results in groups that are no larger than the MaxPageSize value
Second, we can increate MaxPageSize size, but it not recommend, since this change will cause some security risks. For the reason, please see this article:
MaxPageSize is set too high
http://technet.microsoft.com/en-us/library/aa998536(v=exchg.80).aspx
In our case, for your use I increase the MaxPageSize to 2500. If the result still exceed this number you had better to use paged search control solution or alternatively use OU as the search scope.
More information about this issue, please see the below article:
How to view and set LDAP policy in Active Directory by using Ntdsutil.exe
http://support.microsoft.com/kb/315071/en-us
