Reboot your computer. The problem will probably go away. If you are in the habit of having a lot of other programs running, also consider closing them to help conserve system resources.
Remove spyware from your computer.
Make sure there are no problems like looping errors (for example a child linked to himself as his own father, etc.) by doing a Check/Repair of your family file and fixing problems reported on the Error log. Click on File > File Maintenance > Check/Repair and follow the screen prompts to complete the maintenance. Next try what you were doing before.
If the system error continues, try the following steps:
Uninstall and re-install Legacy Family Tree and try Legacy FamilySearch again.
Remove/uninstall programs that you don't use/need.
If the error continues then you can try a system registry repair. There are several utilities available to do this. Some cost money and some are free. We have had success with Ccleaner from Piriform. You can download the free version at https://www.ccleaner.com/ccleaner/download.
If all else fails to fix error code 8:
With Legacy and Legacy FamilySearch closed, browse into C:\Program Files\Legacy\ directory on your hard drive and delete the FamilySearch subfolder.
Replace the FamilySearch folder by updating your Legacy program with this new update at https://legacyfamilytree.com/download-update.
Start Legacy Family Tree and click on File on the menu bar and select File Maintenance > Check/Repair and proceed with the repair. If any error messages occur during the Check/Repair process, click No in the error message box so that the repair steps can finish. Do Check/Repair twice if errors are found. When done close Legacy.
Start Legacy FamilySearch and click on File and select File Maintenance > Check and Repair.
Try FamilySearch again.