Cannot migrate from 5.21.5 to 6.6 or other MX6 version)

Cannot migrate from 5.21.5 to mx 6 I migrate a project from 5.13.1 to 5.21.5 and fixed the errors. Now I want to migrate to MX6 but that is not possible. I get this error: 'project.mpr could not be opened, because it was created with version 5.21.5 of the modeler, which is incompatible with this version of the modeler' Was it not smart to migrate to the latest 5 version (5.21.5)? Hopefully I don't have to start again. Thanks for you response.
1 answers

In the Release Notes of Mendix 6.7.1 I see:

You can now use 6.7.1 for opening 5.21.5 projects (it was not possible to open 5.21.5 projects with 6.7.0). (Ticket 467011) We fixed the conversion issues in the Modeler due to excluded mapping documents.