Yeast contamination in one well - (Jul/25/2011 )

I plated my cells into the wells of a 6-well culture plate and observed contamination (probably yeast) in only one of the wells out of the 6.
How could that happen? Can I continue my experiments on the wells that are not contaminated or should I throw away the entire plate?
Please help!!

I would toss the entire plate out to avoid the risk of it contaminating the other wells.