If attempting to update a lead's milestones in the install tracker causes the error "There was an error saving" "There was an error saving your changes" follow the instructions below.
Ensure the user updating milestones is an admin user from the installer. Installers should be updating milestones.
Click into the Milestone and check if the user attempting the change is the assigned user.
If not, remove the assigned user and save. Leave this field blank.
Once the assigned user has been removed, the milestone should be able to be updated.