Could you please describe what you meant by "Unity version 3.0"? If you mean the version of the spine-unity runtime, then it will for sure not be compatible with assets exported from the Spine Editor version 4.0.64. If you mean the version of the Unity Editor, I assume you were missing the first part of the version number?
Please note that the "Version" field in the export options of the Spine Editor is for importing a project in an older Spine Editor version (and then re-exporting it from e.g. Spine Editor version 3.8.x), not for runtime use.
Which version of the spine-unity runtime are you using? If you're not using the latest available unitypackage from the download page, please have a try whether updating the runtime resolves your issue. As always, back up your project first to be on the safe side.
