Avoiding "a one of the" wrong article use

What kind of error is it?

It's a grammatical error involving the use of articles and determiners.

Why do people make this mistake?

People may make this error due to confusion about article usage and redundancy. They might add "a" unnecessarily before phrases that already start with a determiner like "one of the".

What is correct?

When using a phrase like "one of the", the article "a" is not needed because "one" already functions as a determiner.