You have a column [ID] in the two skills tables. Is this [EmployeeID]? The table definition of users_hierarchy clashes with the later INSERT; which has the correct column name?
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden