As I know this problem often occurs when you use Trados 2011, you can try to repair the problem according to the prompt by Trados 2011, For example, check and add the missed bookmarks. Also , you can try to use Trados 2013 or 2014 to generate the target file if you have them, the problem can often be solved by this way.
Many thanks for your post - it's much appreciated.
I tried and located the segment where the bookmark end was missing in the target. Copied and pasted the tag and problem solved.
Thanks again for your prompt post.