IIS log failed to write entry, File /LM/W3SVC/2/ROOT/global.asa

Hi ,

Am getting below warning message on my Unified Access gateway 2010 server

Warning: IIS log failed to write entry, File /LM/W3SVC/2/ROOT/global.asa Line 31 Object required: 'Request'. .
    Source ="Active Server Pages"

Any idea what does it means.I have checked the global.asa file,and line 31 says

"Sub Session_OnEnd
 if Request.ServerVariables("URL") <> "/WebService.asp" then
      SendLoginMessage(false)
 end if
 set Session("SessionMgr") = Nothing 
 set Session("MonitorMgr") = Nothing"

Can any one please help me to understand why this warning messages and what I can do for this