I didn't watch the game yet so my analysis is based on a scan of the boxscore.
What really lost the game for the Packers was special teams. On Tennessee's first two TD drives, the first started at their 42 yard line, and the second started at their 46 yard line. The Packers were losing the field position battle and giving Tennessee a short field. Culprit no. 1 is P Jon Ryan who average 30.7 yards on 6 punts. Again, I don't know what the situation was for Ryan during those punts, but that yards/punt average sure looks like a stinker. Tennessee's 3rd TD was on a punt return, so the whole special teams unit on that coverage can probably share in the blame on it. Still one bit of bad luck from last season continued to plague them in this game; other teams are automatic on field goals against them. Tennessee was 3-for-3 on FGs and hit from 46 and 51 yards out. In 2006, the only missed field goal against the Packers was a 52 yard attempt against Miami. This isn't about putting pressure on the kicker since such a small percentage of kicks are actually blocked. It's just bad luck that eventually will return to normal.
The second unit defense had their second bad game in a row. Last week Jacksonville was shut out against the first team defense in the 1st half, but scored 21 points in the 2nd half against the second team. At Tennessee, almost the entire 1st team defense sat it out and Tennessee had five scoring drives. Tennessee had a healthy 4.8 yards/carry and their QBs completed over 70% of their passes.
There is no obvious culprit on offense, no one shined in the box score, and it appeared that it stalled after QB Brett Favre left the game because they wanted to see how RB DeShawn Wynn would produce with 20+ carries. The answer is he would average just over 2 yards/carry. That might not his fault, like I've said I didn't watch the game, but that doesn't look good for him.
Despite the ugly score, it still was only a preseason game and the preseason record isn't proof of anything, and there were few injuries, although RB Noah Herron did suffer a knee injury.