I got something similar a few times, but I was called "too perfect" by some girls, including two ex girlfriends. Sounds totally ridiculous to me, but my female friends explained that some (insecure) girls simply don't feel comfortable dating guys who look/dress better than them because it makes them look bad and feel unworthy. It's like guys who put hot girls on pedestals and are intimidated by them basically.
Another thing they told me was that they couldn't feel comfortable sleeping with a guy who had a sixpack because it would make them feel too inferior about their own bodies.
However, "too pretty" might refer to your style. Some girls don't go for the pretty boy/metrosexual type and prefer a more rugged man, just as some guys prefer a feminine woman over a tomboy. Don't worry about it though, if this is the case, it just means your not her type, whereas many girls love that look. And if it's any consolation, I've heard girls say the same thing about David Beckham and Jude Law, among other popular celebrities.