Event ID 2915: [User] has gone over budget

I'm seeing this error on our Exchange 2010 server event log and trying to figure out why a user would be hitting the server over 100 times in a minute. Every reference i find (including a thread here on TechNet) says to change the max concurrency to null. I don't want to disable throttling, I want to know why these users are hitting the box like this.

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Log Name:      Application

Source:        MSExchange ADAccess

Date:          4/7/2011 11:05:14 AM

Event ID:      2915

Task Category: General

Level:         Error

Keywords:      Classic

User:          N/A

Computer:      server

Description:

Process Microsoft.Exchange.RpcClientAccess.Service.exe (PID=2788). User 'user' has gone over budget '109' times for component 'RCA' within a one minute period. Info: 'Policy:DefaultThrottlingPolicy_82c6efd6-110a-4584-b50c-3f2fb749b0cd, Parts:CAS:108;'. Threshold value: '100'.

Event Xml:

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">

  <System>

    <Provider Name="MSExchange ADAccess" />

    <EventID Qualifiers="49152">2915</EventID>

    <Level>2</Level>

    <Task>1</Task>

    <Keywords>0x80000000000000</Keywords>

    <TimeCreated SystemTime="2011-04-07T16:05:14.000000000Z" />

    <EventRecordID>141780</EventRecordID>

    <Channel>Application</Channel>

    <Computer></Computer>

    <Security />

  </System>

  <EventData>

    <Data>Microsoft.Exchange.RpcClientAccess.Service.exe</Data>

    <Data>2788</Data>

    <Data>user</Data>

    <Data>109</Data>

    <Data>RCA</Data>

    <Data>Policy:DefaultThrottlingPolicy_82c6efd6-110a-4584-b50c-3f2fb749b0cd, Parts:CAS:108;</Data>

    <Data>100</Data>

  </EventData>

</Event>

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Anyone found a solution to this yet? Thanks.