# Troubleshooting

Library Preparation > DNA Library Prep > Troubleshooting

* [Overtagmentation of Nextera XT libraries](https://knowledge.illumina.com/library-preparation/dna-library-prep/library-preparation-dna-library-prep-troubleshooting-list/000001054)
* [Undertagmentation of Nextera XT libraries](https://knowledge.illumina.com/library-preparation/dna-library-prep/library-preparation-dna-library-prep-troubleshooting-list/000001148)