An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed.

I'm getting the following error despite customErrors being "Off" in every web.config I can find:

Description:
An application error occurred on the server. The current custom error
settings for this application prevent the details of the application error from
being viewed.

Details: To enable the details of this specific
error message to be viewable on the local server machine, please create a
< customErrors> tag within a "web.config" configuration file located in the
root directory of the current web application. This <customErrors> tag
should then have its "mode" attribute set to "RemoteOnly". To enable the details
to be viewable on remote machines, please set "mode" to "Off".

<!-- Web.Config Configuration File --><configuration><system.web><customErrors mode="RemoteOnly"/></system.web></configuration>

<!-- Web.Config Configuration File --><configuration><system.web><customErrors mode="On" defaultRedirect="mycustompage.htm"/></system.web></configuration>