Are you using IIS 6 or IIS 7? by your Error message and log I feel it is IIS 7 ... but you have posted in an IIS 6 forum ... I am confused... :)
Anyways I will tell you about both of them ....
By default you must remember that at local machine you will get detailed errors... so if you want to check custom errors... best place to check is a remote machine...
However in IIS 7 after you place a custom error message ... click on Edit feature Settings under the Actions pane for Error Pages feature...Under Error responses here select Custom error pages... After doing so you will get to see custom error messages on local machine as well as on remote machine...But I recommend using the 3rd setting once you are done testing your custom error page... suits us IIS Admins well ;)
This setting is not there on IIS 6, I believe, as far as my knowledge goes... There on local machine it displays the default error messages... so you would have to check custom error on remote machines...
Just reproduced your scenario on both my IIS 7 and IIS 6 machines and they work perfectly so you should be all set ...
Hope this helps....
Regards,
MA Khan
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