# App migration, mongoDB error

**URL:** https://forums.rocket.chat/t/app-migration-mongodb-error/3477
**Category:** Community Support
**Created:** [March 27, 2019, 8:29am UTC](https://forums.rocket.chat/t/app-migration-mongodb-error/3477 "2019-03-27T08:29:39Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Marcin](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Marcin](https://forums.rocket.chat/u/Marcin)
#### Post date: [March 27, 2019, 8:29am UTC](https://forums.rocket.chat/t/app-migration-mongodb-error/3477/1 "2019-03-27T08:29:39Z")

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We are trying to change a server.  
During the database loading procedure an error occurs:

* * *

## `2019-03-10T21:26:19.854+0100 Failed: mo1120_rock2.assets.chunks: error creating indexes for mo1120_rock2.assets.chunks: createIndex error: The field 'w' is not valid for an index specification. Specification: { w: 1, name: "files_id_1_n_1", ns: "mo1120_rock2.assets.chunks", key: { files_id: 1, n: 1 } }`

Rocket.Chat v0.74.1 (updated)

Do you know any solution for this problem?

Regards