If you are trying to use sub templates in 10.1.3.3 or you used to have them in previous releases and they are not working for you now ... read on. You are not going mad ... we slipped some new security into the release and by default the security is 'On' and stopping 'external content' from being pulled into your templates.
This property controls whether to use secure file I/O mode for the XSLProcessor and for the XMLParser. When it is set to true, file I/O such as import sub-template or import an XML document is not allowed. Its set via the Admin > Runtime Configuration pages. It can also be set at the report level too.
So, now you know, apologies for any confusion, misery and heartache caused!