Here are some links to sites that discuss troubleshooting protein gels:

http://aldrin.tripod.com/index-3.html

http://www.sigmaaldrich.com/life-science/core-bioreagents/learning-center/troubleshooting-tables.html#Troubleshooting%20Guide%20for%20SDS-PAGE%20Protein%20Electrophoresis

http://web.archive.org/web/20080223110218/www.ruf.rice.edu/~bioslabs/studies/sds-page/sdsgoofs.html