SYMPTOMS
Server Error in '/MyWebApp' Application
Configuration Error
Description: 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: 'mydll'.
Source Error:
Line 169: <add assembly=<System.Drawing, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a>/>
Line 170: <add assembly=<System.EnterpriseServices, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a>/>
Line 171: <add assembly=<*>/>
Line 172: </assemblies>
Line 173:
Source File: c:\winnt\microsoft.net\framework\v1.0.3705\Config\machine.config Line: 171
Version Information: Microsoft .NET Framework Version:1.0.3705.0; ASP.NET Version:1.0.3705.0
This occurs 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.
RESOLUTION
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. To do so, follow these steps:
Click Start, point to All Programs, point to Administrative Tools, and then click Computer Management.
Expand the Services and Applications node, expand the Indexing Service node, and then expand the System node.
Right-click the Directories folder, point to New, and then click Directory from the subform to open the Add Directory dialog box.
Click Browse, and then locate the Temporary ASP.NET Files directory. You typically find the Temporary ASP.NET files in the following path: c:\
Note
Click No under the Include in Index? option buttons.
Click OK to close.
Close the Computer Management dialog box.
Restart the Indexing Services service.
MSDN article :
http://support.microsoft.com/default.aspx?scid=kb;en-us;329065