Maps exported to PNG and GIF formats with the Transparent Color option set may not have transparent pixels

Description

Maps exported to PNG and GIF formats with the Transparent Color option may not have transparent pixels when the export is done at high resolutions or when the image size is large.

Cause

This is a known issue.

Workaround

Note:
This issue is addressed in ArcGIS 9.1 Service Pack 1 (SP1).