It's a good guess that one of your clips is reversed? This would hang some versions of VP, but is now fixed.
Install the latest version. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
If this is not the issue, please share your project. Someone will check it out and suggest or make a fix. It's easy, quick and can be private.
Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
If it contains sensitive material link it in a personal message (PM). Click the envelope above. It won't be passed on or retained. Use FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to share it.