Just run into this issue with Umbraco 6.1.2 where it returns a 'System.IO.DirectoryNotFoundException: Could not find a part of the path' error. When referencing a file relative to a file in the same sub directory.

In 4.x.x, you could reference an include using the following syntax:

<xsl:include href="../templates/_Article.xslt" />
Which would translate to: [xslt]/templates/Article.xslt (e.g. get me something in the XSLT folder)

In 6.1.2, the error says C:\LocalDev\vdb.1020.beth\VS.NET\beth.portfolio.Web\templates\_Gallery.xslt

Noticed the XSLT folder has been dropped.

To work now includes need to be written as:

<xsl:include href="../xslt/templates/_Article.xslt"/>
or
<xsl:include href="templates/_Article.xslt"/>
<xsl:include href="helpers/_MultiPicker.xslt"/> 

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So it looks like when the XSLT processor handles an include, it treats all files as if they are inside "/XSLT", and not a sub folder? Essentially flattening out the file system.

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Is that the desired behavior or is that a bug? It seems a bit explict to me? 

Laurence