Why is it that IIS will not recognize any custom error file other than in 2 locations

[SarahW]

Hi,

Why is it that the system (Windows Server 2003 / IIS v6 / Plesk v8.6) will not recognize any custom error file anywhere other than either in the error_docs folder or in the C:\WINDOWS\Help\iisHelp\common folder. IIS is very happy to use whatever file I specify, as long as the file sits in one of those two folders. If it is anywhere else, then I get an error message that the file cannot be found. Why is that?

Thanks,

Sarah