Installing Office Web Application on SharePoint 2010 after the configuration wizard is through with its process you may ran into an issue on Step 5: Configuring SharePoint services. The configuration wizard failed with an InvalidOperationException with the following entry in the eventlog.
Failed to register SharePoint services. An exception of type System.InvalidOperationException was thrown. Additional exception information: Failed to load or format string Id ManagementUI_ExcelCalculationService_FriendlyName for culture en-US: System.TypeInitializationException: The type initializer for ‘Microsoft.Office.Excel.Server.Host.ExcelServerHost’ threw an exception. —> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. —> System.TypeLoadException: Could not load type ‘Microsoft.Office.Excel.Server.Extensions.IHostExtension’ from assembly ‘Microsoft.Office.Excel.Server.MossHost, Version=184.108.40.206, Culture=neutral, PublicKeyToken=71e9bce111e9429c’.
Click run and type regedit enter goto HKLM\SOFTWARE\MICROSOFT\Shared Tools\Web Server Extensions\14.0\WSS\Services Delete the key for the service causing the error and re-run the configuration. After the delete the coniguration wizard ran successfully to completion.
Please note that by removing above reg. key the Excel Service will appear under SharePoint Central Admin. Configuration. so you may not able to view Excel document online.
help from : http://techdhaan.wordpress.com/