Certainly, I am not expecting anyone debugging .
The syntax ,You saw was just one of syntax I tried. First ,I used exactly same Grid_Motion sample UDF given in the Manual.
After having the interpreting error ; I thought , There could be a mistyping in the Manual Then I tried diferent syntaxs.
Customization Manual Item 4.3 mentiones the same error ; I had; can happen. But not advicing any solution.
So , this error is a systemic error without solution , I am afraid.
The only helping source is you and your colleques that I can rely on.
Many many thanks