# jsonschema.exceptions.RefResolutionError:

**URL:** https://community.blockcerts.org/t/jsonschema-exceptions-refresolutionerror/1330
**Category:** Support
**Created:** [September 5, 2018, 12:26pm UTC](https://community.blockcerts.org/t/jsonschema-exceptions-refresolutionerror/1330 "2018-09-05T12:26:17Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![Hugo](https://sea2.discourse-cdn.com/flex016/user_avatar/community.blockcerts.org/hugo/32/449_2.png) [@Hugo](https://community.blockcerts.org/u/Hugo)
#### Post date: [September 5, 2018, 11:56pm UTC](https://community.blockcerts.org/t/jsonschema-exceptions-refresolutionerror/1330/2 "2018-09-05T23:56:14Z")

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Hello @Taibah

Maybe you are using **python2** when you need **python3**.  
Make sure you are using a virtualenv as explained in the recommendations here: [https://github.com/blockchain-certificates/cert-issuer/blob/master/docs/virtualenv.md](https://github.com/blockchain-certificates/cert-issuer/blob/master/docs/virtualenv.md)

I saw a similar error here: [Error installing cert-issuer on ethereum](https://community.blockcerts.org/t/error-installing-cert-issuer-on-ethereum/1091/10) (which I think could have been solved by installing **python3-dev** ).

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