> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/instrumentation/nextseq-500-550/instrumentation-nextseq-500-550-troubleshooting-list/000001834.md).
# Troubleshooting 'Not Found' error message on NextSeq 500/550
The following error is related to antivirus software (eg, McAfee) considering Illumina's Real-Time Analysis (RTA) as a security threat and archiving the respective executable file (RTA.exe) for quarantine. This error can occur right when the run starts, causing the consumables to be marked as used (and unable to be used for further attempts at starting the run).\
\&#xNAN;***Error message: Not Found (ServiceStack.ServiceClient.Web.WebServiceException)***\
**Troubleshooting steps:**
Follow the guidelines for antivirus configuration in the [Illumina Instrument Control Computer Security and Networking Guide](https://support.illumina.com/downloads/networking-security.html).
* Install the antivirus software only when the instrument is not in use and the instrument can be rebooted.
* Do not allow the computer to reboot automatically after install.
* Set antivirus software to manual scans. **Do not enable automatic scans**.
* Perform manual scans only when the instrument is not in use.
* Set updates to download without user authorization, but not to install.
* Exclude the application directory and data drives from any real-time file system protection.
Windows Defender is off by default and it must remain off. This Windows product can affect the computer resources used by Illumina software.
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| *For any feedback or questions regarding this article (Illumina Knowledge Article #1834), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000001834%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |
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