How to setup a default error template or 404 error template?
ColdFusion MX requires a relative path to your error-handling templates, whereas ColdFusion 5.0 and earlier accepted an absolute path, such as "C:\error\my404.cfm."
The solution is to create a mapping to your error templates. Then, specify this relative path in your missing Template Handler and Site-wide Error Handler fields.
Logical Path: /error
Directory Path: C:\error
missing Template Handler: /error/my404.cfm
Site-wide Error Handler: /error/myError.cfm
As of CF version 6.0 (MX), when you submit these changes in CF Administrator, the "file does not exist" errors WILL APPEAR. This is a BUG. Ignore these warnings and test your templates manually. You'll likely find that they function perfectly.