App stopped working

[Migeria]

I was always testing it while adding multiple files to checkedtextbox1, checking needed ones and on button click they would be added to file. But now even messagebox doesn't show up if I select checkedtextbox item which was added from openFileDialog (if I add folder with folderBrowserDialog or input filename myself, everything works).

Any ideas whats wrong?

#pragma once
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#pragma region Windows Form Designer generated code
//DELETED
#pragma endregion 

[Migeria]

Deleted