Dolby Digital 5.1 and Dolby 2.0

I have been editing a series of clips and 4 of the 5 clips are in Dolby Digital 5.1 Surround but one is only Dolby Digital 2.0. When I attempt to share, Final Cut seems to get hung up. Everything had been processing fine with the 5.1 clips only but once I introduced the 2 channel clips FCP 7 just gets hung up. I am thinking that FCP is having problems processing 5.1 then 2.0 and then back to 5.1 clips. Has anyone else had this problem before, and if so, what their solution might have been?

Thanks!