Why you shouldn't say "try do"

What kind of error is it?

It is a grammatical error related to improper verb usage in English.

Why do people make this mistake?

People often inadvertently omit the infinitive marker "to" when combining verbs, especially when translating directly from other languages that do not require "to" in similar constructions.

What is correct?

After "try", the correct form is either "to" + base verb (to indicate an attempt) or verb-ing (to suggest experimentation).