Hi all,
after struggling some reasonable time with the same issue if found this post. I used background images named like Img16%.jpg and in visual studio design mode they were shown fine but at run time they were ignored. Tests with some more special characters identified another two problematic candidates: & and #.
In total we have now at least 4 characters to avoid in image names: "+", "%", "&" and "#".
Development env. is vwg 6.4.0c, VS2010, IIS5.1(XP)
Regards, Herb