Error importing packages in newer versions.

[Kurt-Dekker]

It looks mostly like you’ve got to deal with TextMeshPro now being part of Unity.

The upgrade guides are here:

Unity - Manual: Upgrading Unity

There’s more notes here:

Migrating from Legacy / Asset Store to Package Manager Releases

As per the title and assuming all goes well, a new version of TextMesh Pro will be included by default in Unity 2018.1. Most likely starting with Beta 2 or Beta 3. (See Updated Notes below about 2018.2 and additional information ) This new version of TMP will be made available via the new Unity Package Manager (also part of Unity 2018.1). These new Unity Package Manager (UPM) packages are shared between all projects. This new version of TMP includes source code and uses the new Assembly Definit…

Fortunately you are never the first to find issues.