Anyone had a problem where the experience has stopped increasing?

I’m in act III and have finished allot of the main quests and have gone in to battlefields. Part the way through my experience has stopped increasing, level 26 experience 6,549,246. Level 27 starts at experience 6,552,000. This either means:
1. There is a max experience or max level allowed for each act. (Hunting through the forum people suggest that you typically get to level 30 by the end, so I can’t be hitting an overall experience or level limit).
2. Something I’ve done in the game has stopped me gaining experience.
3. I’ve found a bug. (I’ve had patch 1.45 loaded a long while ago, so could be something new).

I went back to an older save game and the same thing happens, with just slightly different experience points.

Anyone had a similar problem or have got any suggestions, preferably helpful ones.