# Error Upgrading from 5.6 to 6.6

**URL:** <https://discuss.elastic.co/t/error-upgrading-from-5-6-to-6-6/172381>\
**Category:** Elasticsearch\
**Created:** [March 14, 2019, 4:11pm UTC](https://discuss.elastic.co/t/error-upgrading-from-5-6-to-6-6/172381 "2019-03-14T16:11:08Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![dawiro](https://avatars.discourse-cdn.com/v4/letter/d/71e660/32.png) [@dawiro](https://discuss.elastic.co/u/dawiro)\
**Post date:** [March 14, 2019, 4:11pm UTC](https://discuss.elastic.co/t/error-upgrading-from-5-6-to-6-6/172381/1 "2019-03-14T16:11:08Z")

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Hi,  
I'm exploring upgrading from 5.6.3 (with basic x-pack) to 6.6.2 (basic x-pack built-in) and am seeing an odd error on the master node as the new 6.6.2 master tries to join:

```auto
java.lang.IllegalArgumentException: Unknown NamedWriteable [org.elasticsearch.cluster.metadata.MetaData$Custom][ml]

```

Given that we deploy elasticsearch with machine learning disabled why is this happening? I have no x-pack setting in the elasticsearch.yml of the new node joining the cluster.

Regards,  
D

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [April 11, 2019, 4:11pm UTC](https://discuss.elastic.co/t/error-upgrading-from-5-6-to-6-6/172381/2 "2019-04-11T16:11:24Z")

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Closed on April 11, 2019, 4:11pm UTC

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