IL: The amount paid on your open installment accounts is too low.
An installment account is one with a fixed monthly payment for the life of the loan. Auto loans and student loans are common examples of installment loans. The amount that has been paid down on your open installment accounts is low. People who haven't paid down much of their installment account loan balances are higher credit risks than people who have.
As monthly installment account payments are made, a portion of the outstanding principal balance is reduced, benefitting your score. Whenever possible, further pay down balances on your accounts. Over time this will also have a positive impact on your score.