Probably already a known bug / deliberate feature but when I imported some products that had a '\', '/' or ':' in their names then the site couldn't handle it and gave a log message of "A generic error occurred in GDI+."
I presumed this was related to the picture permissions originally but tracked it to the product names.
Anyhow, I removed the offending products and it works fine now.
It may be that the manual insert of products doesn't allow these characters so apologies if so.
Anyhow, I think it's a fantastic product and is working well for myself.
Cheers