A serious problem has occurred on export

I’m using Cubase 7 pro and every time I try to export my mixdown I get the " a serious problem has occurred" error but only on one specific project I try to do the mixdown, other projects work fine.
any ideas?

Could it be plugin related? Have you tried a realtime export, or vice versa?

thats strange, real time export works fine but on the other way I get this error