# Troubleshooting Wash State Unknown in NextSeq 500/550 Control Software (NCS) v4.0.0

The following warning can appear in NextSeq Control Software (NCS) v4.0.0 after the instrument is rebooted and initialized. The NextSeq Control Software prompts a notification mentioning the wash state is unknown and then allows for either proceeding with a wash or no wash. This error is specific to NCS 4.0.0 and was fixed in Control Software update v4.0.1.

![](/files/STph8Mn2Qr8pjSBmUAlZ)

**Troubleshooting steps:**

* Update the NextSeq Control Software from v4.0.0 to v4.0.1.
* Contact [Illumina Technical Support](https://www.illumina.com/company/contact-us.html#/) for any additional questions.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #2114), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000002114%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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