The following link explains some of the common causes of front loader washer mildew/odor problems and some preventive measures you can try to keep the problem from coming back:
http://www.fixya.com/support/r3608512-getting_rid_front_loader_mildew_odorIt is strongly recommended that you leave the door OPEN between uses to allow the drum to air out. There is some residual water that remains in the drain line and pump after each wash. Since this is the low point of the drainage system, some water will always be there. This is NORMAL. Since these washers have an air tight seal on the door, leaving it shut can cause the water to begin to sour.
NOTE: This does not mean leaving the door open will make the water evaporate. It allows air into the drum to keep it from becoming stagnant.
Check the drain door bellow and drain pump for any debris that may have accumulated and can begin to cause odors. To check and clean the drain pump reservoir, follow the steps in this next link:
http://www.fixya.com/support/r3574284-checking_the_drain_pump_on_a_front_loadeOnce you have checked the drain pump and door area, make sure you are using the proper detergent. Using the wrong type of detergent, or the improper amount, can cause soap scum build up which causes odors.
You can also attempt to run a clean cycle periodically to keep the tub and lines from developing any mildew or odor problems. This is accomplished by running the washer on the hottest setting while empty, using nothhng but a small amount of bleach.
If you have any questions, please post back and let me know. I hope this helps you.