Summary
This article details the error "Unexpected response: 500 InternalServerError. [...] MDLException AttributeNotFound" and how to resolve it.
Article sections:
Symptoms
After creating custom drill-to, the following error is thrown when attempting to run the report:
MDLException
AttributeNotFound
Resolution
Single quotes around the filters are required - i.e. in the example below, the Category MAIN should have single quotes to be 'MAIN'.