How did you draw the custom shape?
You cant draw by grouping lines and fill the result
Try using the freeform tool in the draw > autoshapes >lines menu (or the
curve / scribble tools)

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John Wilson
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http://www.technologytrish.co.uk/ppttipshome.html
> After drawing an shape, the line can be formatted but the Fill button is
> greyed out.
> How do I do a fill of a grouped shape that behave like an autoshape?