I can´t get georrss to work

Hi,

I am using drupal5 with GMap 5.x-1.1-rc1, GMap Macro Builder 5.x-1.1-rc1 and GMap Overlays 5.x-1.x-dev

When I use this macro it works ok:
[gmap zoom=3 |center=40,0 |width=300px |height=200px |control=Small |type=Map ]

But when I use this macro to try to add georss to the macro as explained in the readme
[gmap zoom=3 |center=40,0 |width=300px |height=200px |control=Small |type=Map |overlay=georss:http://slashgeo.org/index.rss ]

I get a warning javascript popup with just this content: "gmap-auto1map-gmap0" and when I close the javascript warning I just get an empty map, without any markers on it.

I have double checked that rss is available.

¿am I doing something wrong or is there any way to solve this??

many thank in advance for any help.