Sometimes when you have worked on a project for a while it will not load anymore or it will crash when it comes to building time. Why? Most often it is because you have added something or changed something important recently.
While this solution seems pretty simple, it is the simplest thing that causes the problems usually. Always try and keep a log of the changes you make on a daily basis if you do not keep a change management system and always be prepared to roll back and always, always keep backups.