Nesting Virtual Groups

Hi All-

I want to know if it is possible to nest virtual groups within portal. I have the groups being created correctly however when I go (in User Administration) to assign parent or child groups to any virtual group I receive two alerts:

-Group attributes successfully modified

-An error occurred while adding group assignments; to see the correct status, perform a new assigned groups search.

.....And no assignment is made. If I try to make the same type of assignment with non-virtual groups, all is OK.

Is this a limitation to virtual groups?

Tim