Porque Genera un error el importador al cargar un archivo grande?

ELMAH muestra lo siguiente:

System.TimeoutException The operation has timed out.

System.TimeoutException: The operation has timed out. at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass41.<begininvokeasynchronousactionmethod>b40(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass39.<>cDisplayClass3b.<begininvokeactionmethodwithfilters>b35() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass51.<invokeactionmethodfilterasynchronously>b4b() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass51.<invokeactionmethodfilterasynchronously>b4b() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass39.<begininvokeactionmethodwithfilters>b38(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass27.<>cDisplayClass2c.<begininvokeaction>b22() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>cDisplayClass27.<begininvokeaction>b24(IAsyncResult asyncResult) at System.Web.Mvc.AsyncController.<>cDisplayClass19.<beginexecutecore>b14(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.<>cDisplayClass4.<makevoiddelegate>b3(IAsyncResult ar) at System.Web.Mvc.AsyncController.EndExecuteCore(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.<>cDisplayClass4.<makevoiddelegate>b3(IAsyncResult ar) at System.Web.Mvc.MvcHandler.<>cDisplayClass6.<>cDisplayClassb.<beginprocessrequest>b4(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.<>cDisplayClass4.<makevoiddelegate>b__3(IAsyncResult ar) at System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)

ALL_HTTP HTTP_CACHE_CONTROL:no-cache, max-age=259200 HTTP_CONNECTION:keep-alive HTTP_PRAGMA:no-cache HTTP_VIA:1.1 Proxy28.enee.hn:3128 (squid/2.6.STABLE21) HTTP_CONTENT_LENGTH:188 HTTP_CONTENT_TYPE:application/x-www-form-urlencoded; charset=UTF-8 HTTP_ACCEPT:/ HTTP_ACCEPT_ENCODING:identity,gzip,deflate HTTP_ACCEPT_LANGUAGE:es-ES,es;q=0.8,en-US;q=0.5,en;q=0.3 HTTP_COOKIE:UsernameCookieKey=; ASP.NET_SessionId=dpvzsdyspclzvwjg02vfguch; .ASPXFORMSAUTH=8B335B73F665F7A5C013F409C439255DC9FB08F95BA0E864721E45D8C00269D3A127AE23ACA9FAC04692C255593F4987B120E6E8600A9B373C434F7B25B7250DBA4460E8DD9F8C1D2412F87010628BEEA1F140DE7A056DFEFD79D84037E5A354E8296AFD9BC7377AB6F9B16DCD6EDABD96A92AEEB826725A4863A04D5FC0BEBF; RequestVerificationToken_L0V2b2x1dGlvbg=fbvl3GiKn1/g5NviW9bb1h6z26xBKqH+W2KP1lA5C/938Zv29wezRUgnvPWNJlCLODfd9Yv0EpnIm+QAZttCNou4JOKRSYNtpkmoX0Bs2tBwMBCODU8iRY0IVkQkXpLZWkpXQHTJ1x9m4eCC56u6iS6clJiZw+TOnltvdRdS0uA= HTTP_HOST:172.21.160.135 HTTP_REFERER:http://172.21.160.135/Evolution/Infrastructure/PlantillaImportacion HTTP_USER_AGENT:Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0 HTTP_X_REQUESTED_WITH:XMLHttpRequest HTTP_X_FORWARDED_FOR:127.0.0.1

ALL_RAW Cache-Control: no-cache, max-age=259200 Connection: keep-alive Pragma: no-cache Via: 1.1 Proxy28.enee.hn:3128 (squid/2.6.STABLE21) Content-Length: 188 Content-Type: application/x-www-form-urlencoded; charset=UTF-8 Accept: / Accept-Encoding: identity,gzip,deflate Accept-Language: es-ES,es;q=0.8,en-US;q=0.5,en;q=0.3 Cookie: UsernameCookieKey=; ASP.NET_SessionId=dpvzsdyspclzvwjg02vfguch; .ASPXFORMSAUTH=8B335B73F665F7A5C013F409C439255DC9FB08F95BA0E864721E45D8C00269D3A127AE23ACA9FAC04692C255593F4987B120E6E8600A9B373C434F7B25B7250DBA4460E8DD9F8C1D2412F87010628BEEA1F140DE7A056DFEFD79D84037E5A354E8296AFD9BC7377AB6F9B16DCD6EDABD96A92AEEB826725A4863A04D5FC0BEBF; RequestVerificationToken_L0V2b2x1dGlvbg=fbvl3GiKn1/g5NviW9bb1h6z26xBKqH+W2KP1lA5C/938Zv29wezRUgnvPWNJlCLODfd9Yv0EpnIm+QAZttCNou4JOKRSYNtpkmoX0Bs2tBwMBCODU8iRY0IVkQkXpLZWkpXQHTJ1x9m4eCC56u6iS6clJiZw+TOnltvdRdS0uA= Host: 172.21.160.135 Referer: http://172.21.160.135/Evolution/Infrastructure/PlantillaImportacion User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0 X-Requested-With: XMLHttpRequest X-Forwarded-For: 127.0.0.1