If your exterior wall is wood construction and not concrete... I have the same problem.
This is what I was told to do..
First you must reduce the humidity of your basement with a dehumidifier.
Second kill any mold that may have started behind the insulation.. make sure the insulation and wood underneath is dry..(put a fan on it for a couple days) then re-install the insulation. Instead of using plastic as a vapor barrier use house wrap.. the same stuff that goes underneath siding on the exterior of your house. Ideally, you would then sheetrock the wall..
Bottom line.. You need to reduce the humidity of your basement and you need a barrier between the warm air of your basement and the outside wall..
NOTE:I did an experiment where I had a section of the exterior wall insulated and sealed with a plastic vapor barrier.. then I had a section of the wall with no plastic vapor barrier just insulation.. after two weeks I checked and found frost under the section "without" the vapor barrier while the section "with" the barrier was dry..
best of luck to you..
and me.. this is my weekend project..