generate_solution does not work

[letsop]

I try to generate the solution for a very simple test notebook with the line command
"nbgrader generate_solution tp6-dev"
and I keep getting the error message "RuntimeError: Mark scheme region detected in a non-grade cell; please make sure all mark scheme regions are within 'Manually graded task' cells."
which is not relevant
Help would be greatly appreciated
M.

[shreve]

Nbgrader is detecting mark schemes in cells they don't belong in within your notebook.

Presumably, that means either you have one, or you've changed the value it is searching for.

# In your notebook
=== BEGIN MARK SCHEME ===
=== END MARK SCHEME ===

# In your config
c.ClearMarkScheme.begin_mark_scheme_delimeter = "something else"
c.ClearMarkScheme.end_mark_scheme_delimeter = "something else"

Can you share the notebook in question? That would help to diagnose the issue.