Train taken out of service - smoke? 20/06/12

I was on the westbound around 0920 this morning and noticed a burning rubber smell between WAN - STR. When the train arrived at Stratford, the driver announced that he will be tipping out due to smoke in the second carriage.

I half wanted to help detrain to get a move on, it takes a lot longer with the dual platform!

Didn't manage to grab the train or leading car number, sorry.

What could have caused this burning rubber smell and smoke?

Thanks!