Is the expression 'asked for a special permission' grammatically correct?

Nouns once solely used in non-count usages often become countified, that is they become used in what become accepted count usages. Zwicky, at Language Log, includes E-mail, spam and slang as nouns that have recently undergone countification. So it is wise to check on whether 'permission' has undergone such a transformation, allowing the count usage (a permission, three permissions), perhaps more idiomatic with 'padding' (a special permission).

There are certainly computer-related examples, but OALD goes further, having:

permission (2) ​[countable, usually plural] an official written statement allowing somebody to do something

• The publisher is responsible for obtaining the necessary permissions to reproduce illustrations.
• The report recommends that all planning permissions for quarrying in national parks should expire in ten years.

It is arguable whether the example in the test really sufficiently fulfils the 'official' caveat mentioned here, and the dictionary does say that this usage is more commonly encountered in the plural form.

Wiktionary goes no further than to say that permission has count and non-count usages, without examining any caveats that attach.

As I'm a septuagenarian native-speaking Oxford grad, and had to check for countness, and still can't decide on whether 'a special permission' is acceptable in this example, I'd say the test is unfair.