# How to resolve 'An unknown error has occurred' critical system errors on the NovaSeq X Series Instruments
NovaSeq X Series Control Software initialization issues that do not fit within the Control Software error reporting structure will present with the following error message:
"Critical system error - An unknown error has occurred. The system may require a restart."
If this error presents during instrument or Control Software initialization, see the following recommendations:
**Troubleshooting Actions**
1. Do not select Shutdown or power cycle the instrument. Instead, select **Exit Application** to close the NovaSeq X Series Control Software.
2. Collect the Control Software Logs from the /usr/local/illumina/logs/novaseq-x-series-control-software directory on the instrument.
3. Contact [Illumina Tech Support](https://www.illumina.com/company/contact-us.html) for next steps.
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