Banners do not display

I am getting this error after I inserted or activated a banner; The banners does also not display at all; it is setup in admin, layout,
Warning: imagepng() [function.imagepng]: Unable to open 'images/graphs/banner_infobox-2.png' for writing in /home2/cristalt/public_html/mall/admin/includes/classes/phplot.php on line 493
I would appreciate some comments on it.

If you are referring to from within the Admin ...

Using your FTP program go to:
/admin/images/graphs

set the permissions to 777 on this directory ...

Next, delete all the files in there except the file:
index.html

Does this work now?

Yes, it removed the error, but I still cannot get the banners to display.

What Banner Group did you assign the banner to?

Is the Banner Active as in a Green icon?

In the Configuration ... Layout Settings ... which Banner Postion did you assign the Banner Group to?

I got it sorted out eventually and assigned the correct banner groups to the correct banner position.

Thanks Linda, You a Star

Thanks for the update ... that can be frustrating when they get mixed up ...