If you run Index Server (Cisvc.exe), then Index Server may rescan the Temporary ASP.NET Files directory while it requests a Microsoft ASP.NET page. Cisvc.exe then holds a lock on the Temporary ASP.NET Files directory for one to five minutes. The length of time of the lock depends on the size of the directory that causes the Aspnet_wp.exeprocess (or W3wp.exe process for applications that run on Microsoft Internet Information Services [IIS] 6.0) to not load the particular DLL. So when you access a page after an AppDomain load, for example, when you modify the Bin directory or the Web.config file on computers running Microsoft Index Services, you may receive the following error message:,
Server Error in '/AppName' Application
Configuration ErrorDescription: An
error occurred during the processing of a configuration file required to service
this request. Please review the specific error details below and modify your
configuration file appropriately.Parser Error Message: Access is denied:
Solution: If you do not use Index Server on the server, you can disable it. If you use Index Server, you can exclude the Temporary ASP.NET Files directory from the folders that the Index Server scans.
source : http://support.microsoft.com/default.aspx?scid=kb;en-us;329065