If so, temporarily disable the plug-in by renaming or removing the iMovie plug-ins folder where the plug-in resides. Then open iMovie again and test to see if the export (or import) succeeds.
For example, older versions of the Slick plug-ins suite may cause this symptom. Gee Three has an update for their Slick plug-ins here. If you have plug-ins from another company, check with the plug-in developer for possible plug-in updates which may resolve this issue.
Important: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.