custom portal theme missing UR/ie6.css
I am having EP 7.0 sp 11. The portal is using BW UME and serving BW reports. I created custom portal desktop/framework/layout/theme for this portal. However, when BW team create a report and upload directly to portal, the iview has error, "/irj/portalapps/com.sap.portal.design.urdesigndata/themes/portal/my_theme_blue/ur/ur_ie6.css" does not exist. Why it is looking for ur_ie6.css in my customized theme? How can I point it to default one from my custom theme? Thanks in advance.
The css file is there in custom theme directory. The customer was able to view the page correctly after clean the cache. Thank you for your reply.