For ErrorUnit to work with your Elmah; add ErrorUnitCentral._Logger = new ErrorUnitLogger(); where your application start code is.
Also remember to add applicationName to your Elmah config <errorLog type= ... applicationName="WebApplication9"/>; or ErrorUnit will not be able to retrieve errors.
http://johngoldinc.com/Help/html/T_ErrorUnit_Interfaces_ILogger.htm
John Gold