Today I found there were lots of logs record into the IIS log file in folder: System32\LogFiles\W3SVC1
Below is a part of these log data
2011-05-27 00:00:41 W3SVC1 127.0.0.1 POST /MSReportServer/ReportExecution2005.asmx - 80 - 127.0.0.1 Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+.NET+CLR+2.0.50727;+.NET+CLR+3.0.04506.648;+.NET+CLR+3.5.21022;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+.NET+CLR+1.1.4322;+CIBA;+OfficeLiveConnector.1.4;+OfficeLivePatch.1.3) 401 2 2148074254
2011-05-27 00:00:41 W3SVC1 127.0.0.1 POST /MSReportServer/ReportExecution2005.asmx - 80 - 127.0.0.1 Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+.NET+CLR+2.0.50727;+.NET+CLR+3.0.04506.648;+.NET+CLR+3.5.21022;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+.NET+CLR+1.1.4322;+CIBA;+OfficeLiveConnector.1.4;+OfficeLivePatch.1.3) 401 1 0
2011-05-27 00:00:41 W3SVC1 127.0.0.1 POST /MSReportServer/ReportExecution2005.asmx - 80 EGSOLAR\jli 127.0.0.1 Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+.NET+CLR+2.0.50727;+.NET+CLR+3.0.04506.648;+.NET+CLR+3.5.21022;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+.NET+CLR+1.1.4322;+CIBA;+OfficeLiveConnector.1.4;+OfficeLivePatch.1.3) 200 0 0
2011-05-27 00:00:41 W3SVC1 172.21.30.30 GET /MSReports/Reserved.ReportViewerWebControl.axd ReportSession=iensxe555vailr2josbqoj55&ControlID=58421d61622346ddb9d866de229f30d2&Culture=2052&UICulture=4&ReportStack=1&OpType=SessionKeepAlive&TimerMethod=KeepAliveMethodctl131TouchSession0&CacheSeed=Fri%20May%2027%2008%3A00%3A41%202011 80 EGSOLAR\jli 172.21.10.169 Mozilla/4.0+(compatible;+MSIE+7.0;+Windows+NT+5.1;+.NET+CLR+2.0.50727;+.NET+CLR+3.0.04506.648;+.NET+CLR+3.5.21022;+.NET+CLR+3.0.4506.2152;+.NET+CLR+3.5.30729;+.NET+CLR+1.1.4322;+CIBA;+OfficeLiveConnector.1.4;+OfficeLivePatch.1.3) 200 0 0
2011-05-27 00:00:44 W3SVC1 172.21.30.30 GET /iisstart.htm - 80 - 172.18.30.61 Mozilla/5.0+(compatible;+PRTG+Network+Monitor+(www.paessler.com);+Windows) 200 0 0
I think this might be caused by the improper setting on the credite setting, you can follow this to check your settings, I hope it will be helpful:
1. Open the SRS Configuration Tool.
2. Go to the Report Server and Report Manager virtual directory tabs and
check the "Apply Default Settings" check box
3. Click "Apply" on both of those pages to reset the VDIR settings.
4. Try it again.
5. If that doesn't work delete the Virtual Directories from IIS and then
use the configuration tool to recreate them from scratch.
6. If THAT doesn't work make sure that the local account that the app pool
is running under has file permissions to all of the files in the
ReportServer and ReportManager directories and their subdirectories.