[MacDV] iMovie 6 - Transitions

[Donald Tully]

Hi Listers - I have been using iMovie HD 6.0.3 quite successfully for  
a long time.  Suddenly, in the middle of building a slide program, I  
am unable to add transitions.  I am getting a quite useless error  
message that states "An unknown error has occurred" each time I try  
to add a transition - either an original Apple or aftermarket type.   
I tried creating a new project with different photos and had the same  
problem. I also tried rebuilding the iMovie preference file several  
times but that didn't resolve the issue.

Any suggestions?  BTW, I am running an Intel Mac 10.4.10.  Thanks for  
your help...