Your best bet is to try to recover the file or replace it with a back up copy if you have a good back up you can revert to. You may need to recover the file, then import the data into a clone of a back up copy without this issue.
Here's a Knowledge Base Article on the subject: http://help.filemaker.com/app/answers/detail/a_id/4829/kw/export%20records
Things to keep in mind about Recover:
While Recover almost always detects and fully corrects any problems with your file...
- The recovered copy may behave differently even if recover reports "no problems found".
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.
And here's a knowledgebase article that you may find useful: What to do when your file is corrupt (KB5421).