Workflow Status "not started" for a workflow started in a SharePoint HostedApp with association form

Hello,

I was trying to implement the association form inside a SharePoint Hosted-app following the instructions here:

https://msdn.microsoft.com/en-us/library/office/dn518136.aspx

The steps were:

1. Created SharePoint Hosted-App Project

2. Created List in Project

3. Created Workflow inside the project

4. Created association form and edited the code following the instructions.

5. Uploaded the app, created an element in the list and started the workflow.

However the Workflow remains in state "not started" and the steps inside the Workflow are not being processed.

Moreover a get inside the workflow the message above the history list:

"One or more field types are not installed properly. Go to the list settings page to delete these fields."

Any help is appreciated!

Many thanx in advance!

Ioannis