rsItemNotFound for Report Models

I have a Sharepoint integrated Reporting Services server. I have created Report models based on Data Sources. I then created Report Builder Reports to make some BI Charts and Graphs. They look great and work fine for a few days then all of a sudden I get a rsItemNotFound error saying it cannot find the Report Model which is clearly there.

An error has occurred during report processing. (rsProcessingAborted)

The item 'IT Reports/PWPDB_Prod_Model.smdl' cannot be found. (rsItemNotFound)

If I open the Report Model from Report Builder it loads the data fields, but also fails to run reports with the same error

If I try to regenerate the model from the library I get an error stating that the model needs to be a generated model.

The model specified must be a generated model.

(rsModelNotGenerated)

Even after rebooting all of the servers in the farm I get the same messages. I can regenerate a model from the data source and it doesn't work. I am seeing no errors in the logs of my app server at all regarding reporting services.

It looks as though I will have to de-integrate Reporting Services as it is not viable for a business critical application.

Please for th elove of Zeus tell me you were able to solve this?

I am getting the exact same error. I have tried everything under the sun to make this work. Any advice?