event ID 8307 perodically appearing

I am getting this event log error on the WFE servers periodically, some days not ar all other days 2 or 3 times.  It never appears on more than one WFE at a time which leeds me to belive its related to what some one is doing possibly in people picker. I set the Sharepoint logs to verbose and it gives me no more information.

Log Name:      Application
Source:        Microsoft-SharePoint Products-SharePoint Foundation
Date:          3/23/2012 3:31:14 PM
Event ID:      8307
Task Category: Claims Authentication
Level:         Error
Keywords:     
User:          NT AUTHORITY\IUSR
Computer:      ServerWFE2.corp.abc.com
Description:
An exception occurred in AD claim provider when calling SPClaimProvider.FillResolveClaim(): Thread was being aborted..
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-SharePoint Products-SharePoint Foundation" Guid="{6fb7e0cd-52e7-47dd-997a-241563931fc2}" />
    <EventID>8307</EventID>
    <Version>14</Version>
    <Level>2</Level>
    <Task>47</Task>
    <Opcode>0</Opcode>
    <Keywords>0x4000000000000000</Keywords>
    <TimeCreated SystemTime="2012-03-23T19:31:14.212Z" />
    <EventRecordID>323474</EventRecordID>
    <Correlation ActivityID="{294BA215-2C18-4E43-B1EB-D43E4A51F7E7}" />
    <Execution ProcessID="6484" ThreadID="8760" />
    <Channel>Application</Channel>
    <Computer>ServerWFE2.corp.abc.com</Computer>
    <Security UserID="S-1-5-17" />
  </System>
  <EventData>
    <Data Name="string0">AD</Data>
    <Data Name="string1">SPClaimProvider.FillResolveClaim()</Data>
    <Data Name="string2">Thread was being aborted.</Data>
  </EventData>
</Event>