Using custom group particles -- problems in 2.49b

I’ve created a group, each member of which is a small png file, image mapped to a plane. I named the group “Chargroup”.
I attach a particle system to an iconosphere, and then go to the “Visualization” panel, set the type as “Group”, and then in the GR: field, type the name of my group, “Chargroup.”

As soon as I press return, or click out of the field, it goes blank, and the link to my group is not completed.

Seems like this should be straightforward. What am I missing?

Thanks in advance for your comments and solutions!