Please make certain that your system has enough memory -- 8 GB is minimum.
Please update your Legacy program.
Current version of Legacy: https://legacyfamilytree.com/download-update
Previous Versions of Legacy: Click Here and download the final release (build) of your version.
If the errors persist, please do the following:
Click File on the menu bar and select Export To from the file menu. Choose Legacy File from the submenu and proceed.
Give the file you will export to a new name and click Save.
The Export screen will open. Please click the large Start Export button. (If you get a message about sources, click Don't Assign a Source.)
Next try Legacy again using the new file and delete the old one when you are satisfied with the results.