I have the same problem. It worked in previous versions of DOSBox but not in 0.74. As ataribaby mentioned, it seems to be related to the sampled voices. It also seems to be Adlib specific: I have no problems starting the mission if the sound is switched to PC speaker or Roland (strangely, I hear the sampled voice with the PC speaker!).

I'm content with not using Adlib, but I can provide debugging information (output from OS X when I force quit DOSBox) if someone really wants to fix this.

If you look at the status window when these hangs occur, you should see a message about DMA segbound wrapping. This has been changed in current source; DOSBox won't terminate, but you'll still get a warning about the wrapping in the status window.

If you would like to keep the AdLib sound but lose the sampled speech (to avoid the error exit), use settings of sbtype=none, oplmode=opl2. I think the game still tries to play the sampled speech through the AdLib, but this is not well supported in DOSBox and will probably be difficult to hear.