HelloCustomer my name is Dan.
Obviously you know how to do this because you had a camera exactly like it.
Can you explain to me more about the stripped-down camera?
Is this a newer version of the Sony camera?
It sounds like either a, there is a problem in iMovie or b, there is corruption in the file itself.
I recommend as a first step, repairing permissions, this is done with Disk Utility found in Applications/Utilities, it looks like this.
Remember, this is a first step and may not solve the problem.
It is however, a good place to start.
If that does not have the desired results, then there are other steps to take.
Let me know please.