Export Audio Mixdown Level Problem

Lately, whenever I try to export an audio mixdown, the levels on the resulting .wav or .mp3 file are MUCH lower than when played back in Cubase 6.55. I shoot for as close to 0db as practical on the main output buss, but the mixdowns barely move the led meters on other players, even on 100% volume. This wasn’t a problem until recently.

Any ideas? Thanks in advance.