A build that produces no lineups is caused by setting lineup constraints that mean that there are no lineups that can be built.
The most common culprits here are:
Min & max salary settings that mean no lineups can be built
Stack, Group, or Aggregate rules that are either invalid or directly conflict with each other
Either the entire, or too much of the player pool being removed such that lineups can’t be built
Too many locked players such that lineups cannot be built
Typically, the easiest way to troubleshoot and resolve this for yourself is to create a new build and start over, adding in your adjustments one at a time or in small batches, attempting to build each time. When you add in an adjustment that causes the build to fail, you know that that is the cause of the issue, and can investigate that adjustment more thoroughly to fix the issue.
Most of the time, it is simply an error in entering your adjustments, and creating a new build and starting over from scratch fixes the issue.