What is the primary cause?

You create a Power Apps app that integrates with Dynamics 365 Customer Service.
You update the app and run solution checker on the original solution. You receive an error stating solution checker cannot export the solution.
You need to determine the primary cause for the issue.
What is the primary cause?
A. The original solution is locked because there is a dependent patch.
B. The solution was not exported before running solution checker.
C. The environment is an Administrator mode.
D. Solution checker cannot check default solutions.