Individual "#" Not Found

This often occurs after importing GEDcoms from sites such as Ancestry, Family Search, etc.

If you have the Deluxe Edition, go to Tools > Renumber RINs.

If you have the Standard Edition, go to File > Export To > Legacy file and export to a new file. Make sure you select the option to renumber the RINs.

You can also run File Maintenance - Check/Repair.  Click on File> File Maintenance > Check/Repair and follow the prompts.
 
If the error messages occur during the Check/Repair process, click No to continue with the repair.  Do step 2 twice if errors are found.