UDF causes fatal error with pattern?

Hello,

I have created a UDF of an obround for use with a mapkey.  The obround has an internal coordinate system and associated planes for a fast, drag and snap placement.  When I place the UDF it is grouped as standard but will not pattern as a group, so I ungroup it and try to pattern but every time it gives a fatal error.  Is there a way around this or am I doing somthing wrong?

Thanks in advance for any help.